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# Autogenerated by Sphinx on Tue Jan 30 18:36:07 2018
topics = {'assert': 'The "assert" statement\n'
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'**********************\n'
'\n'
'Assert statements are a convenient way to insert debugging '
'assertions\n'
'into a program:\n'
'\n'
' assert_stmt ::= "assert" expression ["," expression]\n'
'\n'
'The simple form, "assert expression", is equivalent to\n'
'\n'
' if __debug__:\n'
' if not expression: raise AssertionError\n'
'\n'
'The extended form, "assert expression1, expression2", is '
'equivalent to\n'
'\n'
' if __debug__:\n'
' if not expression1: raise AssertionError(expression2)\n'
'\n'
'These equivalences assume that "__debug__" and "AssertionError" '
'refer\n'
'to the built-in variables with those names. In the current\n'
'implementation, the built-in variable "__debug__" is "True" under\n'
'normal circumstances, "False" when optimization is requested '
'(command\n'
'line option -O). The current code generator emits no code for an\n'
'assert statement when optimization is requested at compile time. '
'Note\n'
'that it is unnecessary to include the source code for the '
'expression\n'
'that failed in the error message; it will be displayed as part of '
'the\n'
'stack trace.\n'
'\n'
'Assignments to "__debug__" are illegal. The value for the '
'built-in\n'
'variable is determined when the interpreter starts.\n',
'assignment': 'Assignment statements\n'
'*********************\n'
'\n'
'Assignment statements are used to (re)bind names to values and '
'to\n'
'modify attributes or items of mutable objects:\n'
'\n'
' assignment_stmt ::= (target_list "=")+ (starred_expression '
'| yield_expression)\n'
' target_list ::= target ("," target)* [","]\n'
' target ::= identifier\n'
' | "(" [target_list] ")"\n'
' | "[" [target_list] "]"\n'
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' | attributeref\n'
' | subscription\n'
' | slicing\n'
' | "*" target\n'
'\n'
'(See section Primaries for the syntax definitions for '
'*attributeref*,\n'
'*subscription*, and *slicing*.)\n'
'\n'
'An assignment statement evaluates the expression list '
'(remember that\n'
'this can be a single expression or a comma-separated list, the '
'latter\n'
'yielding a tuple) and assigns the single resulting object to '
'each of\n'
'the target lists, from left to right.\n'
'\n'
'Assignment is defined recursively depending on the form of the '
'target\n'
'(list). When a target is part of a mutable object (an '
'attribute\n'
'reference, subscription or slicing), the mutable object must\n'
'ultimately perform the assignment and decide about its '
'validity, and\n'
'may raise an exception if the assignment is unacceptable. The '
'rules\n'
'observed by various types and the exceptions raised are given '
'with the\n'
'definition of the object types (see section The standard type\n'
'hierarchy).\n'
'\n'
'Assignment of an object to a target list, optionally enclosed '
'in\n'
'parentheses or square brackets, is recursively defined as '
'follows.\n'
'\n'
'* If the target list is empty: The object must also be an '
'empty\n'
' iterable.\n'
'* If the target list is a single target in parentheses: The '
'object\n'
' is assigned to that target.\n'
'* If the target list is a comma-separated list of targets, or '
'a\n'
' single target in square brackets: The object must be an '
'iterable\n'
' with the same number of items as there are targets in the '
' list, and the items are assigned, from left to right, to '
'the\n'
' corresponding targets.\n'
' * If the target list contains one target prefixed with an\n'
' asterisk, called a "starred" target: The object must be '
'an\n'
' iterable with at least as many items as there are targets '
'in the\n'
' target list, minus one. The first items of the iterable '
'are\n'
' assigned, from left to right, to the targets before the '
'starred\n'
' target. The final items of the iterable are assigned to '
'the\n'
' targets after the starred target. A list of the remaining '
'items\n'
' in the iterable is then assigned to the starred target '
'(the list\n'
' can be empty).\n'
'\n'
' * Else: The object must be an iterable with the same number '
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'of\n'
' items as there are targets in the target list, and the '
'items are\n'
' assigned, from left to right, to the corresponding '
'targets.\n'
'\n'
'Assignment of an object to a single target is recursively '
'defined as\n'
'follows.\n'
'\n'
'* If the target is an identifier (name):\n'
'\n'
' * If the name does not occur in a "global" or "nonlocal" '
'statement\n'
' in the current code block: the name is bound to the object '
'in the\n'
' current local namespace.\n'
'\n'
' * Otherwise: the name is bound to the object in the global\n'
' namespace or the outer namespace determined by '
'"nonlocal",\n'
' respectively.\n'
'\n'
' The name is rebound if it was already bound. This may cause '
'the\n'
' reference count for the object previously bound to the name '
'to reach\n'
' zero, causing the object to be deallocated and its '
'destructor (if it\n'
' has one) to be called.\n'
'\n'
'* If the target is an attribute reference: The primary '
'expression in\n'
' the reference is evaluated. It should yield an object with\n'
' assignable attributes; if this is not the case, "TypeError" '
'is\n'
' raised. That object is then asked to assign the assigned '
'object to\n'
' the given attribute; if it cannot perform the assignment, it '
'raises\n'
' an exception (usually but not necessarily '
'"AttributeError").\n'
'\n'
' Note: If the object is a class instance and the attribute '
'reference\n'
' occurs on both sides of the assignment operator, the RHS '
'expression,\n'
' "a.x" can access either an instance attribute or (if no '
'instance\n'
' attribute exists) a class attribute. The LHS target "a.x" '
'is always\n'
' set as an instance attribute, creating it if necessary. '
'Thus, the\n'
' two occurrences of "a.x" do not necessarily refer to the '
'same\n'
' attribute: if the RHS expression refers to a class '
'attribute, the\n'
' LHS creates a new instance attribute as the target of the\n'
' assignment:\n'
'\n'
' class Cls:\n'
' x = 3 # class variable\n'
' inst = Cls()\n'
' inst.x = inst.x + 1 # writes inst.x as 4 leaving Cls.x '
'as 3\n'
'\n'
' This description does not necessarily apply to descriptor\n'
' attributes, such as properties created with "property()".\n'
'\n'
'* If the target is a subscription: The primary expression in '
'the\n'
' reference is evaluated. It should yield either a mutable '
'sequence\n'
' object (such as a list) or a mapping object (such as a '
'dictionary).\n'
' Next, the subscript expression is evaluated.\n'
'\n'
' If the primary is a mutable sequence object (such as a '
'list), the\n'
' subscript must yield an integer. If it is negative, the '
"sequence's\n"
' length is added to it. The resulting value must be a '
'nonnegative\n'
" integer less than the sequence's length, and the sequence is "
'asked\n'
' to assign the assigned object to its item with that index. '
'If the\n'
' index is out of range, "IndexError" is raised (assignment to '
'a\n'
' subscripted sequence cannot add new items to a list).\n'
'\n'
' If the primary is a mapping object (such as a dictionary), '
'the\n'
" subscript must have a type compatible with the mapping's key "
'type,\n'
' and the mapping is then asked to create a key/datum pair '
'which maps\n'
' the subscript to the assigned object. This can either '
'replace an\n'
' existing key/value pair with the same key value, or insert a '
'new\n'
' key/value pair (if no key with the same value existed).\n'
'\n'
' For user-defined objects, the "__setitem__()" method is '
'called with\n'
' appropriate arguments.\n'
'\n'
'* If the target is a slicing: The primary expression in the\n'
' reference is evaluated. It should yield a mutable sequence '
'object\n'
' (such as a list). The assigned object should be a sequence '
'object\n'
' of the same type. Next, the lower and upper bound '
'expressions are\n'
' evaluated, insofar they are present; defaults are zero and '
'the\n'
" sequence's length. The bounds should evaluate to integers. "
'If\n'
" either bound is negative, the sequence's length is added to "
'it. The\n'
' resulting bounds are clipped to lie between zero and the '
"sequence's\n"
' length, inclusive. Finally, the sequence object is asked to '
'replace\n'
' the slice with the items of the assigned sequence. The '
'length of\n'
' the slice may be different from the length of the assigned '
'sequence,\n'
' thus changing the length of the target sequence, if the '
'target\n'
' sequence allows it.\n'
'\n'
'**CPython implementation detail:** In the current '
'implementation, the\n'
'syntax for targets is taken to be the same as for expressions, '
'and\n'
'invalid syntax is rejected during the code generation phase, '
'causing\n'
'less detailed error messages.\n'
'\n'
'Although the definition of assignment implies that overlaps '
'between\n'
"the left-hand side and the right-hand side are 'simultaneous' "
'(for\n'
'example "a, b = b, a" swaps two variables), overlaps *within* '
'the\n'
'collection of assigned-to variables occur left-to-right, '
'sometimes\n'
'resulting in confusion. For instance, the following program '
'prints\n'
'"[0, 2]":\n'
'\n'
' x = [0, 1]\n'
' i = 0\n'
' i, x[i] = 1, 2 # i is updated, then x[i] is '
'updated\n'
' print(x)\n'
'\n'
'See also:\n'
'\n'
' **PEP 3132** - Extended Iterable Unpacking\n'
' The specification for the "*target" feature.\n'
'\n'
'\n'
'Augmented assignment statements\n'
'===============================\n'
'\n'
'Augmented assignment is the combination, in a single '
'statement, of a\n'
'binary operation and an assignment statement:\n'
'\n'
' augmented_assignment_stmt ::= augtarget augop '
'(expression_list | yield_expression)\n'
' augtarget ::= identifier | attributeref | '
'subscription | slicing\n'
' augop ::= "+=" | "-=" | "*=" | "@=" | '
'"/=" | "//=" | "%=" | "**="\n'
' | ">>=" | "<<=" | "&=" | "^=" | "|="\n'
'\n'
'(See section Primaries for the syntax definitions of the last '
'three\n'
'symbols.)\n'
'\n'
'An augmented assignment evaluates the target (which, unlike '
'normal\n'
'assignment statements, cannot be an unpacking) and the '
'expression\n'
'list, performs the binary operation specific to the type of '
'assignment\n'
'on the two operands, and assigns the result to the original '
'target.\n'
'The target is only evaluated once.\n'
'\n'
'An augmented assignment expression like "x += 1" can be '
'rewritten as\n'
'"x = x + 1" to achieve a similar, but not exactly equal '
'effect. In the\n'
'augmented version, "x" is only evaluated once. Also, when '
'possible,\n'
'the actual operation is performed *in-place*, meaning that '
'rather than\n'
'creating a new object and assigning that to the target, the '
'old object\n'
'is modified instead.\n'
'\n'
'Unlike normal assignments, augmented assignments evaluate the '
'left-\n'
'hand side *before* evaluating the right-hand side. For '
'example, "a[i]\n'
'+= f(x)" first looks-up "a[i]", then it evaluates "f(x)" and '
'performs\n'
'the addition, and lastly, it writes the result back to '
'"a[i]".\n'
'\n'
'With the exception of assigning to tuples and multiple targets '
'in a\n'
'single statement, the assignment done by augmented assignment\n'
'statements is handled the same way as normal assignments. '
'Similarly,\n'
'with the exception of the possible *in-place* behavior, the '
'binary\n'
'operation performed by augmented assignment is the same as the '
'normal\n'
'binary operations.\n'
'\n'
'For targets which are attribute references, the same caveat '
'about\n'
'class and instance attributes applies as for regular '
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'assignments.\n'
'\n'
'\n'
'Annotated assignment statements\n'
'===============================\n'
'\n'
'Annotation assignment is the combination, in a single '
'statement, of a\n'
'variable or attribute annotation and an optional assignment '
'statement:\n'
'\n'
' annotated_assignment_stmt ::= augtarget ":" expression ["=" '
'expression]\n'
'\n'
'The difference from normal Assignment statements is that only '
'single\n'
'target and only single right hand side value is allowed.\n'
'\n'
'For simple names as assignment targets, if in class or module '
'scope,\n'
'the annotations are evaluated and stored in a special class or '
'module\n'
'attribute "__annotations__" that is a dictionary mapping from '
'variable\n'
'names (mangled if private) to evaluated annotations. This '
'attribute is\n'
'writable and is automatically created at the start of class or '
'module\n'
'body execution, if annotations are found statically.\n'
'\n'
'For expressions as assignment targets, the annotations are '
'evaluated\n'
'if in class or module scope, but not stored.\n'
'\n'
'If a name is annotated in a function scope, then this name is '
'local\n'
'for that scope. Annotations are never evaluated and stored in '
'function\n'
'scopes.\n'
'\n'
'If the right hand side is present, an annotated assignment '
'performs\n'
'the actual assignment before evaluating annotations (where\n'
'applicable). If the right hand side is not present for an '
'expression\n'
'target, then the interpreter evaluates the target except for '
'the last\n'
'"__setitem__()" or "__setattr__()" call.\n'
'\n'
'See also: **PEP 526** - Variable and attribute annotation '
'syntax\n'
' **PEP 484** - Type hints\n',
'atom-identifiers': 'Identifiers (Names)\n'
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'*******************\n'
'\n'
'An identifier occurring as an atom is a name. See '
'section Identifiers\n'
'and keywords for lexical definition and section Naming '
'and binding for\n'
'documentation of naming and binding.\n'
'\n'
'When the name is bound to an object, evaluation of the '
'atom yields\n'
'that object. When a name is not bound, an attempt to '
'evaluate it\n'
'raises a "NameError" exception.\n'
'\n'
'**Private name mangling:** When an identifier that '
'textually occurs in\n'
'a class definition begins with two or more underscore '
'characters and\n'
'does not end in two or more underscores, it is '
'considered a *private\n'
'name* of that class. Private names are transformed to a '
'longer form\n'
'before code is generated for them. The transformation '
'inserts the\n'
'class name, with leading underscores removed and a '
'single underscore\n'
'inserted, in front of the name. For example, the '
'identifier "__spam"\n'
'occurring in a class named "Ham" will be transformed to '
'"_Ham__spam".\n'
'This transformation is independent of the syntactical '
'context in which\n'
'the identifier is used. If the transformed name is '
'extremely long\n'
'(longer than 255 characters), implementation defined '
'truncation may\n'
'happen. If the class name consists only of underscores, '
'no\n'
'transformation is done.\n',
'atom-literals': 'Literals\n'
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'********\n'
'\n'
'Python supports string and bytes literals and various '
'numeric\n'
'literals:\n'
'\n'
' literal ::= stringliteral | bytesliteral\n'
' | integer | floatnumber | imagnumber\n'
'\n'
'Evaluation of a literal yields an object of the given type '
'(string,\n'
'bytes, integer, floating point number, complex number) with '
'the given\n'
'value. The value may be approximated in the case of '
'floating point\n'
'and imaginary (complex) literals. See section Literals for '
'details.\n'
'\n'
'All literals correspond to immutable data types, and hence '
'the\n'
"object's identity is less important than its value. "
'Multiple\n'
'evaluations of literals with the same value (either the '
'same\n'
'occurrence in the program text or a different occurrence) '
'may obtain\n'
'the same object or a different object with the same '
'value.\n',
'attribute-access': 'Customizing attribute access\n'
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'****************************\n'
'\n'
'The following methods can be defined to customize the '
'meaning of\n'
'attribute access (use of, assignment to, or deletion of '
'"x.name") for\n'
'class instances.\n'
'\n'
'object.__getattr__(self, name)\n'
'\n'
' Called when an attribute lookup has not found the '
'attribute in the\n'
' usual places (i.e. it is not an instance attribute '
'nor is it found\n'
' in the class tree for "self"). "name" is the '
'attribute name. This\n'
' method should return the (computed) attribute value '
'or raise an\n'
' "AttributeError" exception.\n'
'\n'
' Note that if the attribute is found through the '
'normal mechanism,\n'
' "__getattr__()" is not called. (This is an '
'intentional asymmetry\n'
' between "__getattr__()" and "__setattr__()".) This is '
'done both for\n'
' efficiency reasons and because otherwise '
'"__getattr__()" would have\n'
' no way to access other attributes of the instance. '
'Note that at\n'
' least for instance variables, you can fake total '
'control by not\n'
' inserting any values in the instance attribute '
'dictionary (but\n'
' instead inserting them in another object). See the\n'
' "__getattribute__()" method below for a way to '
'actually get total\n'
' control over attribute access.\n'
'\n'
'object.__getattribute__(self, name)\n'
'\n'
' Called unconditionally to implement attribute '
'accesses for\n'
' instances of the class. If the class also defines '
'"__getattr__()",\n'
' the latter will not be called unless '
'"__getattribute__()" either\n'
' calls it explicitly or raises an "AttributeError". '
'This method\n'
' should return the (computed) attribute value or raise '
'an\n'
' "AttributeError" exception. In order to avoid '
'infinite recursion in\n'
' this method, its implementation should always call '
'the base class\n'
' method with the same name to access any attributes it '
'needs, for\n'
' example, "object.__getattribute__(self, name)".\n'
'\n'
' Note: This method may still be bypassed when looking '
'up special\n'
' methods as the result of implicit invocation via '
'language syntax\n'
' or built-in functions. See Special method lookup.\n'
'\n'
'object.__setattr__(self, name, value)\n'
'\n'
' Called when an attribute assignment is attempted. '
'This is called\n'
' instead of the normal mechanism (i.e. store the value '
'in the\n'
' instance dictionary). *name* is the attribute name, '
'*value* is the\n'
' value to be assigned to it.\n'
'\n'
' If "__setattr__()" wants to assign to an instance '
'attribute, it\n'
' should call the base class method with the same name, '
'for example,\n'
' "object.__setattr__(self, name, value)".\n'
'\n'
'object.__delattr__(self, name)\n'
'\n'
' Like "__setattr__()" but for attribute deletion '
'instead of\n'
' assignment. This should only be implemented if "del '
'obj.name" is\n'
' meaningful for the object.\n'
'\n'
'object.__dir__(self)\n'
'\n'
' Called when "dir()" is called on the object. A '
'sequence must be\n'
' returned. "dir()" converts the returned sequence to a '
'list and\n'
' sorts it.\n'
'\n'
'\n'
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'Customizing module attribute access\n'
'===================================\n'
'\n'
'Special names "__getattr__" and "__dir__" can be also '
'used to\n'
'customize access to module attributes. The "__getattr__" '
'function at\n'
'the module level should accept one argument which is the '
'name of an\n'
'attribute and return the computed value or raise an '
'"AttributeError".\n'
'If an attribute is not found on a module object through '
'the normal\n'
'lookup, i.e. "object.__getattribute__()", then '
'"__getattr__" is\n'
'searched in the module "__dict__" before raising an '
'"AttributeError".\n'
'If found, it is called with the attribute name and the '
'result is\n'
'returned.\n'
'\n'
'The "__dir__" function should accept no arguments, and '
'return a list\n'
'of strings that represents the names accessible on '
'module. If present,\n'
'this function overrides the standard "dir()" search on a '
'module.\n'
'\n'
'For a more fine grained customization of the module '
'behavior (setting\n'
'attributes, properties, etc.), one can set the '
'"__class__" attribute\n'
'of a module object to a subclass of "types.ModuleType". '
'For example:\n'
'\n'
' import sys\n'
' from types import ModuleType\n'
'\n'
' class VerboseModule(ModuleType):\n'
' def __repr__(self):\n'
" return f'Verbose {self.__name__}'\n"
'\n'
' def __setattr__(self, attr, value):\n'
" print(f'Setting {attr}...')\n"
' setattr(self, attr, value)\n'
'\n'
' sys.modules[__name__].__class__ = VerboseModule\n'
'\n'
'Note: Defining module "__getattr__" and setting module '
'"__class__"\n'
' only affect lookups made using the attribute access '
'syntax --\n'
' directly accessing the module globals (whether by code '
'within the\n'
" module, or via a reference to the module's globals "
'dictionary) is\n'
' unaffected.\n'
'\n'
'Changed in version 3.5: "__class__" module attribute is '
'now writable.\n'
'\n'
'New in version 3.7: "__getattr__" and "__dir__" module '
'attributes.\n'
'\n'
'See also:\n'
'\n'
' **PEP 562** - Module __getattr__ and __dir__\n'
' Describes the "__getattr__" and "__dir__" functions '
'on modules.\n'
'\n'
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'Implementing Descriptors\n'
'========================\n'
'\n'
'The following methods only apply when an instance of the '
'class\n'
'containing the method (a so-called *descriptor* class) '
'appears in an\n'
'*owner* class (the descriptor must be in either the '
"owner's class\n"
'dictionary or in the class dictionary for one of its '
'parents). In the\n'
'examples below, "the attribute" refers to the attribute '
'whose name is\n'
"the key of the property in the owner class' "
'"__dict__".\n'
'\n'
'object.__get__(self, instance, owner)\n'
'\n'
' Called to get the attribute of the owner class (class '
'attribute\n'
' access) or of an instance of that class (instance '
'attribute\n'
' access). *owner* is always the owner class, while '
'*instance* is the\n'
' instance that the attribute was accessed through, or '
'"None" when\n'
' the attribute is accessed through the *owner*. This '
'method should\n'
' return the (computed) attribute value or raise an '
'"AttributeError"\n'
' exception.\n'
'\n'
'object.__set__(self, instance, value)\n'
'\n'
' Called to set the attribute on an instance *instance* '
'of the owner\n'
' class to a new value, *value*.\n'
'\n'
'object.__delete__(self, instance)\n'
'\n'
' Called to delete the attribute on an instance '
'*instance* of the\n'
' owner class.\n'
'\n'
'object.__set_name__(self, owner, name)\n'
'\n'
' Called at the time the owning class *owner* is '
'created. The\n'
' descriptor has been assigned to *name*.\n'
'\n'
' New in version 3.6.\n'
'\n'
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'The attribute "__objclass__" is interpreted by the '
'"inspect" module as\n'
'specifying the class where this object was defined '
'(setting this\n'
'appropriately can assist in runtime introspection of '
'dynamic class\n'
'attributes). For callables, it may indicate that an '
'instance of the\n'
'given type (or a subclass) is expected or required as '
'the first\n'
'positional argument (for example, CPython sets this '
'attribute for\n'
'unbound methods that are implemented in C).\n'
'\n'
'\n'
'Invoking Descriptors\n'
'====================\n'
'\n'
'In general, a descriptor is an object attribute with '
'"binding\n'
'behavior", one whose attribute access has been '
'overridden by methods\n'
'in the descriptor protocol: "__get__()", "__set__()", '
'and\n'
'"__delete__()". If any of those methods are defined for '
'an object, it\n'
'is said to be a descriptor.\n'
'\n'
'The default behavior for attribute access is to get, '
'set, or delete\n'
"the attribute from an object's dictionary. For instance, "
'"a.x" has a\n'
'lookup chain starting with "a.__dict__[\'x\']", then\n'
'"type(a).__dict__[\'x\']", and continuing through the '
'base classes of\n'
'"type(a)" excluding metaclasses.\n'
'\n'
'However, if the looked-up value is an object defining '
'one of the\n'
'descriptor methods, then Python may override the default '
'behavior and\n'
'invoke the descriptor method instead. Where this occurs '
'in the\n'
'precedence chain depends on which descriptor methods '
'were defined and\n'
'how they were called.\n'
'\n'
'The starting point for descriptor invocation is a '
'binding, "a.x". How\n'
'the arguments are assembled depends on "a":\n'
'\n'
'Direct Call\n'
' The simplest and least common call is when user code '
'directly\n'
' invokes a descriptor method: "x.__get__(a)".\n'
'\n'
'Instance Binding\n'
' If binding to an object instance, "a.x" is '
'transformed into the\n'
' call: "type(a).__dict__[\'x\'].__get__(a, type(a))".\n'
'\n'
'Class Binding\n'
' If binding to a class, "A.x" is transformed into the '
'call:\n'
' "A.__dict__[\'x\'].__get__(None, A)".\n'
'\n'
'Super Binding\n'
' If "a" is an instance of "super", then the binding '
'"super(B,\n'
' obj).m()" searches "obj.__class__.__mro__" for the '
'base class "A"\n'
' immediately preceding "B" and then invokes the '
'descriptor with the\n'
' call: "A.__dict__[\'m\'].__get__(obj, '
'obj.__class__)".\n'
'\n'
'For instance bindings, the precedence of descriptor '
'invocation depends\n'
'on the which descriptor methods are defined. A '
'descriptor can define\n'
'any combination of "__get__()", "__set__()" and '
'"__delete__()". If it\n'
'does not define "__get__()", then accessing the '
'attribute will return\n'
'the descriptor object itself unless there is a value in '
"the object's\n"
'instance dictionary. If the descriptor defines '
'"__set__()" and/or\n'
'"__delete__()", it is a data descriptor; if it defines '
'neither, it is\n'
'a non-data descriptor. Normally, data descriptors '
'define both\n'
'"__get__()" and "__set__()", while non-data descriptors '
'have just the\n'
'"__get__()" method. Data descriptors with "__set__()" '
'and "__get__()"\n'
'defined always override a redefinition in an instance '
'dictionary. In\n'
'contrast, non-data descriptors can be overridden by '
'instances.\n'
'\n'
'Python methods (including "staticmethod()" and '
'"classmethod()") are\n'
'implemented as non-data descriptors. Accordingly, '
'instances can\n'
'redefine and override methods. This allows individual '
'instances to\n'
'acquire behaviors that differ from other instances of '
'the same class.\n'
'\n'
'The "property()" function is implemented as a data '
'descriptor.\n'
'Accordingly, instances cannot override the behavior of a '
'property.\n'
'\n'
'\n'
'__slots__\n'
'=========\n'
'\n'
'*__slots__* allow us to explicitly declare data members '
'(like\n'
'properties) and deny the creation of *__dict__* and '
'*__weakref__*\n'
'(unless explicitly declared in *__slots__* or available '
'in a parent.)\n'
'The space saved over using *__dict__* can be '
'significant.\n'
'\n'
'object.__slots__\n'
'\n'
' This class variable can be assigned a string, '
'iterable, or sequence\n'
' of strings with variable names used by instances. '
'*__slots__*\n'
' reserves space for the declared variables and '
'prevents the\n'
' automatic creation of *__dict__* and *__weakref__* '
'for each\n'
' instance.\n'
'\n'
'\n'
'Notes on using *__slots__*\n'
'--------------------------\n'
'\n'
'* When inheriting from a class without *__slots__*, the '
'*__dict__*\n'
' and *__weakref__* attribute of the instances will '
'always be\n'
' accessible.\n'
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'\n'
'* Without a *__dict__* variable, instances cannot be '
'assigned new\n'
' variables not listed in the *__slots__* definition. '
'Attempts to\n'
' assign to an unlisted variable name raises '
'"AttributeError". If\n'
' dynamic assignment of new variables is desired, then '
'add\n'
' "\'__dict__\'" to the sequence of strings in the '
'*__slots__*\n'
' declaration.\n'
'\n'
'* Without a *__weakref__* variable for each instance, '
'classes\n'
' defining *__slots__* do not support weak references to '
'its\n'
' instances. If weak reference support is needed, then '
'add\n'
' "\'__weakref__\'" to the sequence of strings in the '
'*__slots__*\n'
' declaration.\n'
'\n'
'* *__slots__* are implemented at the class level by '
'creating\n'
' descriptors (Implementing Descriptors) for each '
'variable name. As a\n'
' result, class attributes cannot be used to set default '
'values for\n'
' instance variables defined by *__slots__*; otherwise, '
'the class\n'
' attribute would overwrite the descriptor assignment.\n'
'\n'
'* The action of a *__slots__* declaration is not limited '
'to the\n'
' class where it is defined. *__slots__* declared in '
'parents are\n'
' available in child classes. However, child subclasses '
'will get a\n'
' *__dict__* and *__weakref__* unless they also define '
'*__slots__*\n'
' (which should only contain names of any *additional* '
'slots).\n'
'\n'
'* If a class defines a slot also defined in a base '
'class, the\n'
' instance variable defined by the base class slot is '
'inaccessible\n'
' (except by retrieving its descriptor directly from the '
'base class).\n'
' This renders the meaning of the program undefined. In '
'the future, a\n'
' check may be added to prevent this.\n'
'\n'
'* Nonempty *__slots__* does not work for classes derived '
'from\n'
' "variable-length" built-in types such as "int", '
'"bytes" and "tuple".\n'
'\n'
'* Any non-string iterable may be assigned to '
'*__slots__*. Mappings\n'
' may also be used; however, in the future, special '
'meaning may be\n'
' assigned to the values corresponding to each key.\n'
'\n'
'* *__class__* assignment works only if both classes have '
'the same\n'
' *__slots__*.\n'
'\n'
'* Multiple inheritance with multiple slotted parent '
'classes can be\n'
' used, but only one parent is allowed to have '
'attributes created by\n'
' slots (the other bases must have empty slot layouts) - '
'violations\n'
' raise "TypeError".\n',
'attribute-references': 'Attribute references\n'
'********************\n'
'\n'
'An attribute reference is a primary followed by a '
'period and a name:\n'
'\n'
' attributeref ::= primary "." identifier\n'
'\n'
'The primary must evaluate to an object of a type '
'that supports\n'
'attribute references, which most objects do. This '
'object is then\n'
'asked to produce the attribute whose name is the '
'identifier. This\n'
'production can be customized by overriding the '
'"__getattr__()" method.\n'
'If this attribute is not available, the exception '
'"AttributeError" is\n'
'raised. Otherwise, the type and value of the object '
'produced is\n'
'determined by the object. Multiple evaluations of '
'the same attribute\n'
'reference may yield different objects.\n',
'augassign': 'Augmented assignment statements\n'
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'*******************************\n'
'\n'
'Augmented assignment is the combination, in a single statement, '
'of a\n'
'binary operation and an assignment statement:\n'
'\n'
' augmented_assignment_stmt ::= augtarget augop '
'(expression_list | yield_expression)\n'
' augtarget ::= identifier | attributeref | '
'subscription | slicing\n'
' augop ::= "+=" | "-=" | "*=" | "@=" | '
'"/=" | "//=" | "%=" | "**="\n'
' | ">>=" | "<<=" | "&=" | "^=" | "|="\n'
'\n'
'(See section Primaries for the syntax definitions of the last '
'three\n'
'symbols.)\n'
'\n'
'An augmented assignment evaluates the target (which, unlike '
'normal\n'
'assignment statements, cannot be an unpacking) and the '
'expression\n'
'list, performs the binary operation specific to the type of '
'assignment\n'
'on the two operands, and assigns the result to the original '
'target.\n'
'The target is only evaluated once.\n'
'\n'
'An augmented assignment expression like "x += 1" can be '
'rewritten as\n'
'"x = x + 1" to achieve a similar, but not exactly equal effect. '
'In the\n'
'augmented version, "x" is only evaluated once. Also, when '
'possible,\n'
'the actual operation is performed *in-place*, meaning that '
'rather than\n'
'creating a new object and assigning that to the target, the old '
'object\n'
'is modified instead.\n'
'\n'
'Unlike normal assignments, augmented assignments evaluate the '
'left-\n'
'hand side *before* evaluating the right-hand side. For '
'example, "a[i]\n'
'+= f(x)" first looks-up "a[i]", then it evaluates "f(x)" and '
'performs\n'
'the addition, and lastly, it writes the result back to "a[i]".\n'
'\n'
'With the exception of assigning to tuples and multiple targets '
'in a\n'
'single statement, the assignment done by augmented assignment\n'
'statements is handled the same way as normal assignments. '
'Similarly,\n'
'with the exception of the possible *in-place* behavior, the '