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Python Official Glossary

Return to Python glossary, Python glossaries, Python jargon, Python terms, Python lingo, Python

# and Symbols

Python default prompt - »> - The default Python prompt of the interactive shell. Often seen for code examples which can be executed interactively in the interpreter.“ (POG 2022)

Python ellipsis - … - Can refer to: The default Python prompt of the interactive shell when entering the code for an indented code block, when within a pair of matching left and right delimiters (parentheses, square brackets, curly braces or triple quotes), or after specifying a decorator. The Ellipsis built-in constant.” (POG 2022)

Python 2to3 - A tool that tries to convert Python 2.x code to Python 3.x code by handling most of the incompatibilities which can be detected by parsing the source code and traversing the parse tree. 2to3 is available in the Python standard library as lib2to3; a standalone entry point is provided as Tools/scripts/2to3. See also 2to3 - Automated Python 2 to 3 code translation.“ (POG 2022)

A

Python abstract base class - Python Abstract base classes complement Python duck-typing by providing a way to define Python interfaces when other techniques like Python hasattr() would be clumsy or subtly wrong (for example with Python magic methods). Python ABCs introduce Python virtual subclasses, which are Python classes that don’t Python inherit from a Python class but are still recognized by Python isinstance() and Python issubclass(); see the Python abc module Python documentation. Python comes with many Python built-in ABCs for Python data structures (in the Python collections.abc module), Python numbers (in the Python numbers module), Python streams (in the Python io module), Python import finders and Python loaders (in the Python importlib.abc module). You can create your own Python ABCs with the Python abc module.” (POG 2022)

Python annotation - A label associated with a variable, a class attribute or a function parameter or return value, used by convention as a type hint. Annotations of local variables cannot be accessed at runtime, but annotations of global variables, class attributes, and functions are stored in the __annotations__ special attribute of modules, classes, and functions, respectively. See variable annotation, function annotation, PEP 484 and PEP 526, which describe this functionality. Also see Annotations Best Practices for best practices on working with annotations.“ (POG 2022)

Python argument - A value passed to a function (or method) when calling the function. There are two kinds of argument:

Python keyword argument: an argument preceded by an identifier (e.g. name=) in a function call or passed as a value in a dictionary preceded by **. For example, 3 and 5 are both keyword arguments in the following calls to complex():

complex(real=3, imag=5) complex(**{'real': 3, 'imag': 5}) positional argument: an argument that is not a keyword argument. Positional arguments can appear at the beginning of an argument list and/or be passed as elements of an iterable preceded by *. For example, 3 and 5 are both positional arguments in the following calls:

complex(3, 5) complex(*(3, 5)) Arguments are assigned to the named local variables in a function body. See the evaluated value is assigned to the local variable. See also the [[Python parameter glossary entry, the Python FAQ question on the difference between arguments and parameters, and PEP 362.” (POG 2022)

Python asynchronous context manager - An object which controls the environment seen in an async with statement by defining __aenter__() and __aexit__() methods. Introduced by PEP 492.“ (POG 2022)

Python asynchronous generator - A function which returns an asynchronous generator iterator. It looks like a coroutine function defined with async def except that it contains yield expressions for producing a series of values usable in an async for loop.” (POG 2022)

Usually refers to an asynchronous generator function, but may refer to an asynchronous generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity.“ (POG 2022)

An asynchronous generator function may contain await expressions as well as async for, and async with statements.” (POG 2022)

Python asynchronous generator iterator - An object created by a asynchronous generator function.“ (POG 2022)

This is an asynchronous iterator which when called using the __anext__() method returns an awaitable object which will execute the body of the asynchronous generator function until the next yield expression.” (POG 2022)

Each yield temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the asynchronous generator iterator effectively resumes with another awaitable returned by __anext__(), it picks up where it left off. See PEP 492 and PEP 525.“ (POG 2022)

Python asynchronous iterable - An object, that can be used in an async for statement. Must return an asynchronous iterator from its __aiter__() method. Introduced by PEP 492.” (POG 2022)

Python asynchronous iterator - An object that implements the __aiter__() and __anext__() methods. __anext__ must return an awaitable object. async for resolves the awaitables returned by an asynchronous iterator’s __anext__() method until it raises a StopAsyncIteration exception. Introduced by PEP 492.“ (POG 2022)

Python attribute - A value associated with an object which is referenced by name using dotted expressions. For example, if an object o has an attribute a it would be referenced as o.a.” (POG 2022)

Python awaitable - An object that can be used in an await expression. Can be a coroutine or an object with an __await__() method. See also PEP 492.“ (POG 2022)

B

Python BDFL - Benevolent Dictator For Life, a.k.a. Guido van Rossum, Python’s creator.” (POG 2022)

Python binary file - A file object able to read and write bytes-like objects. Examples of binary files are files opened in binary mode ('rb', 'wb' or 'rb+'), sys.stdin.buffer, sys.stdout.buffer, and instances of io.BytesIO and gzip.GzipFile. See also text file for a file object able to read and write str objects." ([[POG 2022)

Python borrowed reference - In Python’s C API, a borrowed reference is a reference to an object. It does not modify the object reference count. It becomes a dangling pointer if the object is destroyed. For example, a garbage collection can remove the last strong reference to the object and so destroy it.“ (POG 2022)

Calling Py_INCREF() on the borrowed reference is recommended to convert it to a strong reference in-place, except when the object cannot be destroyed before the last usage of the borrowed reference. The Py_NewRef() function can be used to create a new strong reference.” (POG 2022)

Python bytes-like object - An object that supports the Buffer Protocol and can export a C-contiguous buffer. This includes all bytes, bytearray, and array.array objects, as well as many common memoryview objects. Bytes-like objects can be used for various operations that work with binary data; these include compression, saving to a binary file, and sending over a socket.“ (POG 2022)

Some operations need the binary data to be mutable. The documentation often refers to these as “read-write bytes-like objects”. Example mutable buffer objects include bytearray and a memoryview of a bytearray. Other operations require the binary data to be stored in immutable objects (“read-only bytes-like objects”); examples of these include bytes and a memoryview of a bytes object.” (POG 2022)

Python bytecode - Python source code is compiled into bytecode, the internal representation of a Python program in the CPython interpreter. The bytecode is also cached in .pyc files so that executing the same file is faster the second time (recompilation from source to bytecode can be avoided). This “intermediate language” is said to run on a virtual machine that executes the machine code corresponding to each bytecode. Do note that bytecodes are not expected to work between different Python virtual machines, nor to be stable between Python releases. A list of bytecode instructions can be found in the documentation for the dis module.“ (POG 2022)

C

Python callback - A subroutine function which is passed as an argument to be executed at some point in the future.” (POG 2022)

Python class - A template for creating user-defined objects. Class definitions normally contain method definitions which operate on instances of the class.“ (POG 2022)

Python class variable - A variable defined in a class and intended to be modified only at class level (i.e., not in an instance of the class).” (POG 2022)

Python coercion - The implicit conversion of an instance of one type to another during an operation which involves two arguments of the same type. For example, int(3.15) converts the floating point number to the integer 3, but in 3+4.5, each argument is of a different type (one int, one float), and both must be converted to the same type before they can be added or it will raise a TypeError. Without coercion, all arguments of even compatible types would have to be normalized to the same value by the programmer, e.g., float(3)+4.5 rather than just 3+4.5.“ (POG 2022)

Python complex number - An extension of the familiar real number system in which all numbers are expressed as a sum of a real part and an imaginary part. Imaginary numbers are real multiples of the imaginary unit (the square root of -1), often written i in mathematics or j in engineering. Python has built-in support for complex numbers, which are written with this latter notation; the imaginary part is written with a j suffix, e.g., 3+1j. To get access to complex equivalents of the math module, use cmath. Use of complex numbers is a fairly advanced mathematical feature. If you’re not aware of a need for them, it’s almost certain you can safely ignore them.” (POG 2022)

Python context manager - An object which controls the environment seen in a with statement by defining __enter__() and __exit__() methods. See PEP 343.“ (POG 2022)

Python context variable - A variable which can have different values depending on its context. This is similar to Thread-Local Storage in which each execution thread may have a different value for a variable. However, with context variables, there may be several contexts in one execution thread and the main usage for context variables is to keep track of variables in concurrent asynchronous tasks. See contextvars.” (POG 2022)

Python contiguous - A buffer is considered contiguous exactly if it is either C-contiguous or Fortran contiguous. Zero-dimensional buffers are C and Fortran contiguous. In one-dimensional arrays, the items must be laid out in memory next to each other, in order of increasing indexes starting from zero. In multidimensional C-contiguous arrays, the last index varies the fastest when visiting items in order of memory address. However, in Fortran contiguous arrays, the first index varies the fastest.“ (POG 2022)

Python coroutine - Coroutines are a more generalized form of subroutines. Subroutines are entered at one point and exited at another point. Coroutines can be entered, exited, and resumed at many different points. They can be implemented with the async def statement. See also PEP 492.” (POG 2022)

Python coroutine function - A function which returns a coroutine object. A coroutine function may be defined with the async def statement, and may contain await, async for, and async with keywords. These were introduced by PEP 492.“ (POG 2022)

Python CPython - The canonical implementation of the Python programming language, as distributed on python.org. The term “CPython” is used when necessary to distinguish this implementation from others such as Jython or IronPython.” (POG 2022)

D

Python decorator - A function returning another function, usually applied as a function transformation using the @wrapper syntax. Common examples for decorators are classmethod() and staticmethod().“ (POG 2022)

The decorator syntax is merely syntactic sugar, the following two function definitions are semantically equivalent:

def f(arg):

...

f = staticmethod(f)

@staticmethod def f(arg):

...

The same concept exists for classes, but is less commonly used there. See the documentation for function definitions and class definitions for more about decorators.” (POG 2022)

Python descriptor - Any object which defines the methods __get__(), __set__(), or __delete__(). When a class attribute is a descriptor, its special binding behavior is triggered upon attribute lookup. Normally, using a.b to get, set or delete an attribute looks up the object named b in the class dictionary for a, but if b is a descriptor, the respective descriptor method gets called. Understanding descriptors is a key to a deep understanding of Python because they are the basis for many features including functions, methods, properties, class methods, static methods, and reference to super classes. For more information about descriptors’ methods, see Implementing Descriptors or the Descriptor How To Guide.“ (POG 2022)

Python dictionary - An associative array, where arbitrary keys are mapped to values. The keys can be any object with __hash__() and __eq__() methods. Called a hash in Perl.” (POG 2022)

Python dictionary comprehension - A compact way to process all or part of the elements in an iterable and return a dictionary with the results. results = {n: n ** 2 for n in range(10)} generates a dictionary containing key n mapped to value n ** 2. See Displays for lists, sets and dictionaries." ([[POG 2022)

Python dictionary view - The objects returned from dict.keys(), dict.values(), and dict.items() are called dictionary views. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes. To force the dictionary view to become a full list use list(dictview). See Dictionary view objects.“ (POG 2022)

Python docstring - A string literal which appears as the first expression in a class, function or module. While ignored when the suite is executed, it is recognized by the compiler and put into the __doc__ attribute of the enclosing class, function or module. Since it is available via introspection, it is the canonical place for documentation of the object.” (POG 2022)

Python duck-typing - A programming style which does not look at an object’s type to determine if it has the right interface; instead, the method or attribute is simply called or used (“If it looks like a duck and quacks like a duck, it must be a duck.”) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type() or isinstance(). (Note, however, that duck-typing can be complemented with abstract base classes.) Instead, it typically employs hasattr() tests or EAFP programming.“ (POG 2022)

E

Python EAFP - Easier to ask for forgiveness than permission. This common Python coding style assumes the existence of valid keys or attributes and catches exceptions if the assumption proves false. This clean and fast style is characterized by the presence of many try and except statements. The technique contrasts with the LBYL style common to many other languages such as C.” (POG 2022)

Python expression - A piece of syntax which can be evaluated to some value. In other words, an expression is an accumulation of expression elements like literals, names, attribute access, operators or function calls which all return a value. In contrast to many other languages, not all language constructs are expressions. There are also statements which cannot be used as expressions, such as while. Assignments are also statements, not expressions.“ (POG 2022)

Python extension module - A module written in C or C++, using Python’s C API to interact with the core and with user code.” (POG 2022)

F

Python f-string - String literals prefixed with 'f' or 'F' are commonly called “f-strings” which is short for formatted string literals. See also PEP 498.“ (POG 2022)

Python file object - An object exposing a file-oriented API (with methods such as read() or write()) to an underlying resource. Depending on the way it was created, a file object can mediate access to a real on-disk file or to another type of storage or communication device (for example standard input/output, in-memory buffers, sockets, pipes, etc.). File objects are also called file-like objects or streams.” (POG 2022)

There are actually three categories of file objects: raw binary files, buffered binary files and text files. Their interfaces are defined in the io module. The canonical way to create a file object is by using the open() function.“ (POG 2022)

Python file-like object - A synonym for file object.” (POG 2022)

Python filesystem encoding and error handler - Encoding and error handler used by Python to decode bytes from the operating system and encode Unicode to the operating system.“ (POG 2022)

“The filesystem encoding must guarantee to successfully decode all bytes below 128. If the file system encoding fails to provide this guarantee, API functions can raise UnicodeError.” (POG 2022)

The sys.getfilesystemencoding() and sys.getfilesystemencodeerrors() functions can be used to get the filesystem encoding and error handler.” (POG 2022)

The filesystem encoding and error handler are configured at Python startup by the PyConfig_Read() function: see filesystem_encoding and filesystem_errors members of PyConfig.“ (POG 2022)

G

Python garbage collection - The process of freeing memory when it is not used anymore. Python performs garbage collection via reference counting and a cyclic garbage collector that is able to detect and break reference cycles. The garbage collector can be controlled using the gc module.“ (POG 2022)

Python generator - A function which returns a generator iterator. It looks like a normal function except that it contains yield expressions for producing a series of values usable in a for-loop or that can be retrieved one at a time with the next() function.” (POG 2022)

Usually refers to a generator function, but may refer to a generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity.“ (POG 2022)

Python generator iterator - An object created by a generator function. Each yield temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the generator iterator resumes, it picks up where it left off (in contrast to functions which start fresh on every invocation).” (POG 2022)

Python generator expression - An expression that returns an iterator. It looks like a normal expression followed by a for clause defining a loop variable, range, and an optional if clause. The combined expression generates values for an enclosing function:“ (POG 2022)

sum(i*i for i in range(10)) # sum of squares 0, 1, 4, … 81

285

Python generic function - A function composed of multiple functions implementing the same operation for different types. Which implementation should be used during a call is determined by the dispatch algorithm. See also the Python single dispatch glossary entry, the functools.singledispatch() decorator, and PEP 443.” (POG 2022)

Python generic type - A type that can be parameterized; typically a container class such as list or dict. Used for type hints and annotations. For more details, see generic alias types, PEP 483, PEP 484, PEP 585, and the Python typing module.“ (POG 2022)

Python GIL] - See global interpreter lock.” (POG 2022)

Python global interpreter lock - The mechanism used by the CPython interpreter to assure that only one Python thread executes Python bytecode at a time. This simplifies the CPython implementation by making the Python object model (including critical Python built-in types such as Python dict) implicitly safe against concurrent access. Locking the entire interpreter makes it easier for the interpreter to be Python multi-threaded, at the expense of much of the Python parallelism afforded by multi-processor machines.“ (POG 2022)

However, some extension modules, either standard or third-party, are designed so as to release the GIL when doing computationally-intensive tasks such as compression or hashing. Also, the GIL is always released when doing I/O.” (POG 2022)

Past efforts to create a “free-threaded” interpreter (one which locks shared data at a much finer granularity) have not been successful because performance suffered in the common single-processor case. It is believed that overcoming this performance issue would make the implementation much more complicated and therefore costlier to maintain.“ (POG 2022)

H

Python hash-based pyc - A bytecode cache file that uses the hash rather than the last-modified time of the corresponding source file to determine its validity. See Cached bytecode invalidation." ([[POG 2022)

Python hashable - An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() method). Hashable objects which compare equal must have the same hash value.” (POG 2022)

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.“ (POG 2022)

Most of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not; immutable containers (such as tuples and frozensets) are only hashable if their elements are hashable. Objects which are instances of user-defined classes are hashable by default. They all compare unequal (except with themselves), and their hash value is derived from their id().” (POG 2022)

I

Python IDLE - An Integrated Development Environment for Python. IDLE is a basic editor and interpreter environment which ships with the standard distribution of Python.“ (POG 2022)

Python immutable - An object with a fixed value. Immutable objects include numbers, strings and tuples. Such an object cannot be altered. A new object has to be created if a different value has to be stored. They play an important role in places where a constant hash value is needed, for example as a key in a dictionary.” (POG 2022)

Python import path - A list of locations (or path entries) that are searched by the path based finder for modules to import. During import, this list of locations usually comes from sys.path, but for subpackages it may also come from the parent package’s __path__ attribute.“ (POG 2022)

Python importing - The process by which Python code in one module is made available to Python code in another module.” (POG 2022)

Python importer - An object that both finds and loads a module; both a finder and loader object.“ (POG 2022)

Python interactive - Python has an interactive interpreter which means you can enter statements and expressions at the interpreter prompt, immediately execute them and see their results. Just launch python with no arguments (possibly by selecting it from your computer’s main menu). It is a very powerful way to test out new ideas or inspect modules and packages (remember help(x)).” (POG 2022)

Python interpreted - Python is an interpreted language, as opposed to a compiled one, though the distinction can be blurry because of the presence of the bytecode compiler. This means that source files can be run directly without explicitly creating an executable which is then run. Interpreted languages typically have a shorter development/debug cycle than compiled ones, though their programs generally also run more slowly. See also Python interactive.“ (POG 2022)

Python interpreter shutdown - When asked to shut down, the Python interpreter enters a special phase where it gradually releases all allocated resources, such as modules and various critical internal structures. It also makes several calls to the garbage collector. This can trigger the execution of code in user-defined destructors or weakref callbacks. Code executed during the shutdown phase can encounter various exceptions as the resources it relies on may not function anymore (common examples are library modules or the warnings machinery).” (POG 2022)

“The main reason for interpreter shutdown is that the __main__ module or the script being run has finished executing.” (POG 2022)

Python iterable - An object capable of returning its members one at a time. Examples of iterables include all sequence types (such as list, str, and tuple) and some non-sequence types like dict, file objects, and objects of any classes you define with an __iter__() method or with a __getitem__() method that implements Sequence semantics.“ (POG 2022)

“Iterables can be used in a for loop and in many other places where a sequence is needed (zip(), map(), …). When an iterable object is passed as an argument to the built-in function iter(), it returns an iterator for the object. This iterator is good for one pass over the set of values. When using iterables, it is usually not necessary to call iter() or deal with iterator objects yourself. The for statement does that automatically for you, creating a temporary unnamed variable to hold the iterator for the duration of the loop. See also Python iterator, Python sequence, and Python generator.” (POG 2022)

Python iterator - An object representing a stream of data. Repeated calls to the iterator’s __next__() method (or passing it to the built-in function next()) return successive items in the stream. When no more data are available a StopIteration exception is raised instead. At this point, the iterator object is exhausted and any further calls to its __next__() method just raise StopIteration again. Iterators are required to have an __iter__() method that returns the iterator object itself so every iterator is also iterable and may be used in most places where other iterables are accepted. One notable exception is code which attempts multiple iteration passes. A container object (such as a list) produces a fresh new iterator each time you pass it to the iter() function or use it in a for loop. Attempting this with an iterator will just return the same exhausted iterator object used in the previous iteration pass, making it appear like an empty container. More information can be found in Iterator Types.” (POG 2022)

“CPython implementation detail: CPython does not consistently apply the requirement that an iterator define __iter__().” (POG 2022)

K

Python key function - A key function or collation function is a callable that returns a value used for sorting or ordering. For example, locale.strxfrm() is used to produce a sort key that is aware of locale specific sort conventions.“ (POG 2022)

A number of tools in Python accept key functions to control how elements are ordered or grouped. They include min(), max(), sorted(), list.sort(), heapq.merge(), heapq.nsmallest(), heapq.nlargest(), and itertools.groupby().” (POG 2022)

There are several ways to create a key function. For example. the str.lower() method can serve as a key function for case insensitive sorts. Alternatively, a key function can be built from a lambda expression such as lambda r: (r[0], r[2]). Also, the operator module provides three key function constructors: attrgetter(), itemgetter(), and methodcaller(). See the Sorting HOW TO for examples of how to create and use key functions.“ (POG 2022)

Python eyword argument - See argument.” (POG 2022)

L

Python lambda - An anonymous inline function consisting of a single expression which is evaluated when the function is called. The syntax to create a lambda function is lambda [parameters]: expression“ (POG 2022)

Python LBYL - Look before you leap. This coding style explicitly tests for pre-conditions before making calls or lookups. This style contrasts with the EAFP approach and is characterized by the presence of many if statements.” (POG 2022)

In a multi-threaded environment, the LBYL approach can risk introducing a race condition between “the looking” and “the leaping”. For example, the code, if key in mapping: return mapping[key] can fail if another thread removes key from mapping after the test, but before the lookup. This issue can be solved with locks or by using the EAFP approach.“ (POG 2022)

Python locale encoding - On Unix, it is the encoding of the LC_CTYPE locale. It can be set with locale.setlocale(locale.LC_CTYPE, new_locale). On Windows, it is the ANSI code page (ex: cp1252). locale.getpreferredencoding(False) can be used to get the locale encoding. Python uses the filesystem encoding and error handler to convert between Unicode filenames and bytes filenames.” (POG 2022)

Python list - A built-in Python sequence. Despite its name it is more akin to an array in other languages than to a linked list since access to elements is O(1).“ (POG 2022)

Python list comprehension - A compact way to process all or part of the elements in a sequence and return a list with the results. result = ['{:#04x}'.format(x) for x in range(256) if x % 2 == 0] generates a list of strings containing even hex numbers (0x..) in the range from 0 to 255. The if clause is optional. If omitted, all elements in range(256) are processed.” (POG 2022)

Python loader - An object that loads a module. It must define a method named load_module(). A loader is typically returned by a finder. See PEP 302 for details and importlib.abc.Loader for an abstract base class." ([[POG 2022)

M

Python magic method - An informal synonym for special method.“ (POG 2022)

Python mapping - A container object that supports arbitrary key lookups and implements the methods specified in the Mapping or MutableMapping abstract base classes. Examples include dict, collections.defaultdict, collections.OrderedDict and collections.Counter.” (POG 2022)

Python meta path finder - A finder returned by a search of sys.meta_path. Meta path finders are related to, but different from path entry finders. See importlib.abc.MetaPathFinder for the methods that meta path finders implement." ([[POG 2022)

Python metaclass - The class of a class. Class definitions create a class name, a class dictionary, and a list of base classes. The metaclass is responsible for taking those three arguments and creating the class. Most object oriented programming languages provide a default implementation. What makes Python special is that it is possible to create custom metaclasses. Most users never need this tool, but when the need arises, metaclasses can provide powerful, elegant solutions. They have been used for logging attribute access, adding thread-safety, tracking object creation, implementing singletons, and many other tasks. More information can be found in Python Metaclasses.“ (POG 2022)

Python method - A function which is defined inside a class body. If called as an attribute of an instance of that class, the method will get the instance object as its first argument (which is usually called self). See Python function and nested scope.” (POG 2022)

Python method resolution order - Method Resolution Order is the order in which base classes are searched for a member during lookup. See The Python 2.3 Method Resolution Order for details of the algorithm used by the Python interpreter since the 2.3 release." ([[POG 2022)

Python module - An object that serves as an organizational unit of Python code. Modules have a namespace containing arbitrary Python objects. Modules are loaded into Python by the process of importing. See also Python package.“ (POG 2022)

Python module spec - A namespace containing the import-related information used to load a module. An instance of importlib.machinery.ModuleSpec.” (POG 2022)

Python MRO - See method resolution order.“ (POG 2022)

Python mutable - Mutable objects can change their value but keep their id(). See also Python immutable.” (POG 2022)

N

Python named tuple - The term “named tuple” applies to any type or class that inherits from tuple and whose indexable elements are also accessible using named attributes. The type or class may have other features as well.“ (POG 2022)

Several built-in types are named tuples, including the values returned by time.localtime() and os.stat(). Another example is sys.float_info:” (POG 2022)

sys.float_info[1] # indexed access

1024

sys.float_info.max_exp # named field access

1024

isinstance(sys.float_info, tuple) # kind of tuple

True

“Some named tuples are built-in types (such as the above examples). Alternatively, a named tuple can be created from a regular class definition that inherits from tuple and that defines named fields. Such a class can be written by hand or it can be created with the factory function collections.namedtuple(). The latter technique also adds some extra methods that may not be found in hand-written or built-in named tuples.” (POG 2022)

Python namespace - The place where a variable is stored. Namespaces are implemented as dictionaries. There are the local, global and built-in namespaces as well as nested namespaces in objects (in methods). Namespaces support modularity by preventing naming conflicts. For instance, the functions builtins.open and os.open() are distinguished by their namespaces. Namespaces also aid readability and maintainability by making it clear which module implements a function. For instance, writing random.seed() or itertools.islice() makes it clear that those functions are implemented by the random and itertools modules, respectively.“ (POG 2022)

Python namespace package - A PEP 420 package which serves only as a container for subpackages. Namespace packages may have no physical representation, and specifically are not like a regular package because they have no __init__.py file. See also [[Python module.” (POG 2022)

Python nested scope - The ability to refer to a variable in an enclosing definition. For instance, a function defined inside another function can refer to variables in the outer function. Note that nested scopes by default work only for reference and not for assignment. Local variables both read and write in the innermost scope. Likewise, global variables read and write to the global namespace. The nonlocal allows writing to outer scopes.“ (POG 2022)

Python new-style class - Old name for the flavor of classes now used for all class objects. In earlier Python versions, only new-style classes could use Python’s newer, versatile features like __slots__, descriptors, properties, __getattribute__(), class methods, and static methods.” (POG 2022)

O

Python object -Any data with state (attributes or value) and defined behavior (methods). Also the ultimate base class of any new-style class.“ (POG 2022)

P

Python package - A Python module which can contain submodules or recursively, subpackages. Technically, a package is a Python module with an __path__ attribute. See also Python regular package and Python namespace package.” (POG 2022)

Python parameter - A named entity in a function (or method) definition that specifies an argument (or in some cases, arguments) that the function can accept. There are five kinds of parameter:
- Python positional-or-keyword parameter: specifies an argument that can be passed either positionally or as a keyword argument. This is the default kind of parameter, for example foo and bar in the following: def func(foo, bar=None): …
- Python positional-only parameter: specifies an argument that can be supplied only by position. Positional-only parameters can be defined by including a / character in the parameter list of the function definition after them, for example posonly1 and posonly2 in the following:“ (POG 2022) def func(posonly1, posonly2, /, positional_or_keyword): …
- Python keyword-only parameter: specifies an argument that can be supplied only by keyword. Keyword-only parameters can be defined by including a single var-positional parameter or bare * in the parameter list of the function definition before them, for example kw_only1 and kw_only2 in the following:” (POG 2022) def func(arg, *, kw_only1, kw_only2): …
- Python var-positional parameter: specifies that an arbitrary sequence of positional arguments can be provided (in addition to any positional arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with *, for example args in the following:“ (POG 2022) def func(*args, **kwargs): …
- Python var-keyword parameter: specifies that arbitrarily many keyword arguments can be provided (in addition to any keyword arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with **, for example kwargs in the example above.” (POG 2022)

Parameters can specify both optional and required arguments, as well as default values for some optional arguments.“ (POG 2022)

See also the Python argument glossary entry, the Python FAQ question on the difference between arguments and parameters, the inspect.Parameter class, the Python function definitions section, and PEP 362.

Python path entry - A single location on the import path which the path based finder consults to find modules for importing.” (POG 2022)

Python path entry finder - A finder returned by a callable on sys.path_hooks (i.e. a path entry hook) which knows how to locate modules given a path entry. See importlib.abc.PathEntryFinder for the methods that path entry finders implement." ([[POG 2022)

Python path entry hook - A callable on the sys.path_hook list which returns a path entry finder if it knows how to find modules on a specific path entry.“ (POG 2022)

Python path based finder - One of the default meta path finders which searches an import path for modules.” (POG 2022)

Python path-like object - An object representing a file system path. A path-like object is either a str or bytes object representing a path, or an object implementing the os.PathLike protocol. An object that supports the os.PathLike protocol can be converted to a str or bytes file system path by calling the os.fspath() function; os.fsdecode() and os.fsencode() can be used to guarantee a str or bytes result instead, respectively. Introduced by PEP 519.“ (POG 2022)

Python PEP - Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python or its processes or environment. PEPs should provide a concise technical specification and a rationale for proposed features." ([[POG 2022)

“PEPs are intended to be the primary mechanisms for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions. See PEP 1.” (POG 2022)

Python portion - A set of files in a single directory (possibly stored in a zip file) that contribute to a namespace package, as defined in PEP 420.” (POG 2022)

Python positional argument - See argument.“ (POG 2022)

Python provisional API - A provisional API is one which has been deliberately excluded from the standard library’s backwards compatibility guarantees. While major changes to such interfaces are not expected, as long as they are marked provisional, backwards incompatible changes (up to and including removal of the interface) may occur if deemed necessary by core developers. Such changes will not be made gratuitously – they will occur only if serious fundamental flaws are uncovered that were missed prior to the inclusion of the API.” (POG 2022)

“Even for provisional APIs, backwards incompatible changes are seen as a “solution of last resort” - every attempt will still be made to find a backwards compatible resolution to any identified problems.” (POG 2022)

“This process allows the standard library to continue to evolve over time, without locking in problematic design errors for extended periods of time. See PEP 411 for more details.” (POG 2022)

Python provisional package - See Python provisional API.“ (POG 2022)

Python Python 3000 - Nickname for the Python 3.x release line (coined long ago when the release of version 3 was something in the distant future.) This is also abbreviated “Py3k”.” (POG 2022)

Python Pythonic - An idea or piece of code which closely follows the most common idioms of the Python language, rather than implementing code using concepts common to other languages. For example, a common idiom in Python is to loop over all elements of an iterable using a for statement. Many other languages don’t have this type of construct, so people unfamiliar with Python sometimes use a numerical counter instead:“ (POG 2022)

for i in range(len(food)):

   print(food[i])

As opposed to the cleaner, Pythonic method:

for piece in food:

   print(piece)

qualified name

A dotted name showing the “path” from a module’s global scope to a class, function or method defined in that module, as defined in PEP 3155. For top-level functions and classes, the qualified name is the same as the object’s name:” (POG 2022)

class C:

… class D: … def meth(self): … pass …

C.__qualname__

'C'

C.D.__qualname__

'C.D'

C.D.meth.__qualname__

'C.D.meth'

When used to refer to modules, the fully qualified name means the entire dotted path to the module, including any parent packages, e.g. email.mime.text:“ (POG 2022)

import email.mime.text
email.mime.text.__name__

'email.mime.text'

R

Python reference count - The number of references to an object. When the reference count of an object drops to zero, it is deallocated. Reference counting is generally not visible to Python code, but it is a key element of the CPython implementation. The sys module defines a getrefcount() function that programmers can call to return the reference count for a particular object.” (POG 2022)

Python regular package - A traditional package, such as a directory containing an __init__.py file. See also Python namespace package.“ (POG 2022)

S

Python __slots__ - A declaration inside a class that saves memory by pre-declaring space for instance attributes and eliminating instance dictionaries. Though popular, the technique is somewhat tricky to get right and is best reserved for rare cases where there are large numbers of instances in a memory-critical application.” (POG 2022)

Python sequence - An iterable which supports efficient element access using integer indices via the __getitem__() special method and defines a __len__() method that returns the length of the sequence. Some built-in sequence types are list, str, tuple, and bytes. Note that dict also supports __getitem__() and __len__(), but is considered a mapping rather than a sequence because the lookups use arbitrary immutable keys rather than integers.“ (POG 2022)

The collections.abc.Sequence abstract base class defines a much richer interface that goes beyond just __getitem__() and __len__(), adding count(), index(), __contains__(), and __reversed__(). Types that implement this expanded interface can be registered explicitly using register().” (POG 2022)

Python set comprehension - A compact way to process all or part of the elements in an iterable and return a set with the results. results = {c for c in 'abracadabra' if c not in 'abc'} generates the set of strings {'r', 'd'}. See Displays for lists, sets and dictionaries." ([[POG 2022)

Python single dispatch - A form of generic function dispatch where the implementation is chosen based on the type of a single argument.“ (POG 2022)

Python slice - An object usually containing a portion of a sequence. A slice is created using the subscript notation, [] with colons between numbers when several are given, such as in variable_name[1:3:5]. The bracket (subscript) notation uses slice objects internally.” (POG 2022)

Python special method - A method that is called implicitly by Python to execute a certain operation on a type, such as addition. Such methods have names starting and ending with double underscores. Special methods are documented in Special method names.“ (POG 2022)

Python statement - A statement is part of a suite (a “block” of code). A statement is either an expression or one of several constructs with a keyword, such as if, while or for.” (POG 2022)

Python strong reference - In Python’s C API, a strong reference is a reference to an object which increments the object’s reference count when it is created and decrements the object’s reference count when it is deleted.“ (POG 2022)

“The Py_NewRef() function can be used to create a strong reference to an object. Usually, the Py_DECREF() function must be called on the strong reference before exiting the scope of the strong reference, to avoid leaking one reference. See also Python borrowed reference.” (POG 2022)

T

Python text encoding - A codec which encodes Unicode strings to bytes.” (POG 2022)

Python text file - A file object able to read and write str objects. Often, a text file actually accesses a byte-oriented datastream and handles the text encoding automatically. Examples of text files are files opened in text mode ('r' or 'w'), sys.stdin, sys.stdout, and instances of io.StringIO. See also binary file for a file object able to read and write bytes-like objects.“ (POG 2022)

Python triple-quoted string - A string which is bound by three instances of either a quotation mark (”) or an apostrophe (‘). While they don’t provide any functionality not available with single-quoted strings, they are useful for a number of reasons. They allow you to include unescaped single and double quotes within a string and they can span multiple lines without the use of the continuation character, making them especially useful when writing docstrings.” (POG 2022)

Python type - The type of a Python object determines what kind of object it is; every object has a type. An object’s type is accessible as its __class__ attribute or can be retrieved with type(obj).“ (POG 2022)

Python type alias - A synonym for a type, created by assigning the type to an identifier. Type aliases are useful for simplifying type hints. For example:” (POG 2022)

def remove_gray_shades(

       colors: list[tuple[int, int, int]]) -> list[tuple[int, int, int]]:
   pass

could be made more readable like this:

Color = tuple[int, int, int]

def remove_gray_shades(colors: list[Color]) → list[Color]:

   pass

See Python typing and PEP 484, which describe this functionality.“ (POG 2022)

Python type hint - An annotation that specifies the expected type for a variable, a class attribute, or a function parameter or return value. Type hints are optional and are not enforced by Python but they are useful to static type analysis tools, and aid IDEs with code completion and refactoring. Type hints of global variables, class attributes, and functions, but not local variables, can be accessed using typing.get_type_hints(). See Python typing and PEP 484, which describe this functionality.” (POG 2022)

U

Python universal newlines - A manner of interpreting text streams in which all of the following are recognized as ending a line: the Unix end-of-line convention '\n', the Windows convention '\r\n', and the old Macintosh convention '\r'. See PEP 278 and PEP 3116, as well as bytes.splitlines() for an additional use.“ (POG 2022)

V

Python variable annotation - An annotation of a variable or a class attribute. When annotating a variable or a class attribute, assignment is optional:” (POG 2022)

class C:

   field: 'annotation'

Variable annotations are usually used for type hints: for example this variable is expected to take int values:

count: int = 0 Variable annotation syntax is explained in section Annotated assignment statements.

See function annotation, [[PEP 484 and PEP 526, which describe this functionality. Also see Python Annotations Best Practices for best practices on working with annotations.“ (POG 2022)

Python virtual environment - A cooperatively isolated runtime environment that allows Python users and applications to install and upgrade Python distribution packages without interfering with the behaviour of other Python applications running on the same system. See also Python venv.” (POG 2022)

Python virtual machine - A computer defined entirely in software. Python’s virtual machine executes the Python bytecode emitted by the Python bytecode compiler.“ (POG 2022)

Z

Python Zen of Python - Listing of Python design principles and philosophies that are helpful in understanding and using the language. The listing can be found by typing “import this” at the interactive prompt.” (POG 2022)

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Last updated on Apr 26, 2022.