Compound statements contain (groups of) other statements; they affect or control the execution of those other statements in some way. In general, compound statements span multiple lines, although in simple incarnations a whole compound statement may be contained in one line. Show
The , and statements implement traditional control flow constructs. specifies exception handlers and/or cleanup code for a group of statements, while the statement allows the execution of initialization and finalization code around a block of code. Function and class definitions are also syntactically compound statements. A compound statement consists of one or more ‘clauses.’ A clause consists of a header and a ‘suite.’ The clause headers of a particular compound statement are all at the same indentation level. Each clause header begins with a uniquely identifying keyword and ends with a colon. A suite is a group of statements controlled by a clause. A suite can be one or more semicolon-separated simple statements on the same line as the header, following the header’s colon, or it can be one or more indented statements on subsequent lines. Only the latter form of a suite can contain nested compound statements; the following is illegal, mostly because it wouldn’t be clear to which clause a following clause would belong: if test1: if test2: print(x) Also note that the semicolon binds tighter than the colon in this context, so that in the following example, either all or none of the calls are executed: if x < y < z: print(x); print(y); print(z) Summarizing: compound_stmt ::= Note that statements always end in a for i in range(10): print(i) i = 5 # this will not affect the for-loop # because i will be overwritten with the next # index in the range0 possibly followed by a for i in range(10): print(i) i = 5 # this will not affect the for-loop # because i will be overwritten with the next # index in the range1. Also note that optional continuation clauses always begin with a keyword that cannot start a statement, thus there are no ambiguities (the ‘dangling ’ problem is solved in Python by requiring nested statements to be indented). The formatting of the grammar rules in the following sections places each clause on a separate line for clarity. 8.1. The for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 2 statementThe statement is used for conditional execution: if_stmt ::= "if" It selects exactly one of the suites by evaluating the expressions one by one until one is found to be true (see section for the definition of true and false); then that suite is executed (and no other part of the statement is executed or evaluated). If all expressions are false, the suite of the clause, if present, is executed. 8.2. The for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 3 statementThe statement is used for repeated execution as long as an expression is true: while_stmt ::= "while" This repeatedly tests the expression and, if it is true, executes the first suite; if the expression is false (which may be the first time it is tested) the suite of the for_stmt ::= "for"8 clause, if present, is executed and the loop terminates. A statement executed in the first suite terminates the loop without executing the for_stmt ::= "for"8 clause’s suite. A statement executed in the first suite skips the rest of the suite and goes back to testing the expression. 8.3. The for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 4 statementThe statement is used to iterate over the elements of a sequence (such as a string, tuple or list) or other iterable object: for_stmt ::= "for" The try_stmt ::=6 expression is evaluated once; it should yield an object. An is created for that iterable. The first item provided by the iterator is then assigned to the target list using the standard rules for assignments (see ), and the suite is executed. This repeats for each item provided by the iterator. When the iterator is exhausted, the suite in the for_stmt ::= "for"8 clause, if present, is executed, and the loop terminates. A statement executed in the first suite terminates the loop without executing the for_stmt ::= "for"8 clause’s suite. A statement executed in the first suite skips the rest of the suite and continues with the next item, or with the for_stmt ::= "for"8 clause if there is no next item. The for-loop makes assignments to the variables in the target list. This overwrites all previous assignments to those variables including those made in the suite of the for-loop: for i in range(10): print(i) i = 5 # this will not affect the for-loop # because i will be overwritten with the next # index in the range Names in the target list are not deleted when the loop is finished, but if the sequence is empty, they will not have been assigned to at all by the loop. Hint: the built-in function returns an iterator of integers suitable to emulate the effect of Pascal’s except E as N: foo3; e.g., except E as N: foo4 returns the list except E as N: foo5. Changed in version 3.11: Starred elements are now allowed in the expression list. 8.4. The for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 5 statementThe for_stmt ::= "for"5 statement specifies exception handlers and/or cleanup code for a group of statements: try_stmt ::= Additional information on exceptions can be found in section , and information on using the statement to generate exceptions may be found in section . 8.4.1. except E as N: foo 9 clauseThe except E as N: foo9 clause(s) specify one or more exception handlers. When no exception occurs in the clause, no exception handler is executed. When an exception occurs in the for_stmt ::= "for"5 suite, a search for an exception handler is started. This search inspects the except E as N: foo9 clauses in turn until one is found that matches the exception. An expression-less except E as N: foo9 clause, if present, must be last; it matches any exception. For an except E as N: foo9 clause with an expression, that expression is evaluated, and the clause matches the exception if the resulting object is “compatible” with the exception. An object is compatible with an exception if the object is the class or a of the exception object, or a tuple containing an item that is the class or a non-virtual base class of the exception object. If no except E as N: foo9 clause matches the exception, the search for an exception handler continues in the surrounding code and on the invocation stack. If the evaluation of an expression in the header of an except E as N: foo9 clause raises an exception, the original search for a handler is canceled and a search starts for the new exception in the surrounding code and on the call stack (it is treated as if the entire statement raised the exception). When a matching except E as N: foo9 clause is found, the exception is assigned to the target specified after the if x < y < z: print(x); print(y); print(z)00 keyword in that except E as N: foo9 clause, if present, and the except E as N: foo9 clause’s suite is executed. All except E as N: foo9 clauses must have an executable block. When the end of this block is reached, execution continues normally after the entire statement. (This means that if two nested handlers exist for the same exception, and the exception occurs in the for_stmt ::= "for"5 clause of the inner handler, the outer handler will not handle the exception.) When an exception has been assigned using if x < y < z: print(x); print(y); print(z)06, it is cleared at the end of the except E as N: foo9 clause. This is as if except E as N: foo was translated to except E as N: try: foo finally: del N This means the exception must be assigned to a different name to be able to refer to it after the except E as N: foo9 clause. Exceptions are cleared because with the traceback attached to them, they form a reference cycle with the stack frame, keeping all locals in that frame alive until the next garbage collection occurs. Before an except E as N: foo9 clause’s suite is executed, details about the exception are stored in the module and can be accessed via . returns a 3-tuple consisting of the exception class, the exception instance and a traceback object (see section ) identifying the point in the program where the exception occurred. The details about the exception accessed via are restored to their previous values when leaving an exception handler: if x < y < z: print(x); print(y); print(z)0 8.4.2. if x < y < z: print(x); print(y); print(z) 14 clauseThe if x < y < z: print(x); print(y); print(z)14 clause(s) are used for handling s. The exception type for matching is interpreted as in the case of , but in the case of exception groups we can have partial matches when the type matches some of the exceptions in the group. This means that multiple if x < y < z: print(x); print(y); print(z)14 clauses can execute, each handling part of the exception group. Each clause executes at most once and handles an exception group of all matching exceptions. Each exception in the group is handled by at most one if x < y < z: print(x); print(y); print(z)14 clause, the first that matches it. if x < y < z: print(x); print(y); print(z)1 Any remaining exceptions that were not handled by any if x < y < z: print(x); print(y); print(z)14 clause are re-raised at the end, combined into an exception group along with all exceptions that were raised from within if x < y < z: print(x); print(y); print(z)14 clauses. If the raised exception is not an exception group and its type matches one of the if x < y < z: print(x); print(y); print(z)14 clauses, it is caught and wrapped by an exception group with an empty message string. if x < y < z: print(x); print(y); print(z)2 An if x < y < z: print(x); print(y); print(z)14 clause must have a matching type, and this type cannot be a subclass of . It is not possible to mix and if x < y < z: print(x); print(y); print(z)14 in the same . , and cannot appear in an if x < y < z: print(x); print(y); print(z)14 clause. 8.4.3. for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 8 clauseThe optional for_stmt ::= "for"8 clause is executed if the control flow leaves the suite, no exception was raised, and no , , or statement was executed. Exceptions in the for_stmt ::= "for"8 clause are not handled by the preceding clauses. 8.4.4. if x < y < z: print(x); print(y); print(z) 40 clauseIf if x < y < z: print(x); print(y); print(z)40 is present, it specifies a ‘cleanup’ handler. The clause is executed, including any and clauses. If an exception occurs in any of the clauses and is not handled, the exception is temporarily saved. The if x < y < z: print(x); print(y); print(z)40 clause is executed. If there is a saved exception it is re-raised at the end of the if x < y < z: print(x); print(y); print(z)40 clause. If the if x < y < z: print(x); print(y); print(z)40 clause raises another exception, the saved exception is set as the context of the new exception. If the if x < y < z: print(x); print(y); print(z)40 clause executes a , or statement, the saved exception is discarded: if x < y < z: print(x); print(y); print(z)3 The exception information is not available to the program during execution of the if x < y < z: print(x); print(y); print(z)40 clause. When a , or statement is executed in the suite of a for_stmt ::= "for"5… if x < y < z: print(x); print(y); print(z)40 statement, the if x < y < z: print(x); print(y); print(z)40 clause is also executed ‘on the way out.’ The return value of a function is determined by the last statement executed. Since the if x < y < z: print(x); print(y); print(z)40 clause always executes, a if x < y < z: print(x); print(y); print(z)30 statement executed in the if x < y < z: print(x); print(y); print(z)40 clause will always be the last one executed: if x < y < z: print(x); print(y); print(z)4 Changed in version 3.8: Prior to Python 3.8, a statement was illegal in the if x < y < z: print(x); print(y); print(z)40 clause due to a problem with the implementation. 8.5. The for_stmt ::= "for" target_list "in" starred_list ":" suite ["else" ":" suite] 6 statementThe statement is used to wrap the execution of a block with methods defined by a context manager (see section ). This allows common …… usage patterns to be encapsulated for convenient reuse. if x < y < z: print(x); print(y); print(z)5 The execution of the statement with one “item” proceeds as follows:
The following code: if x < y < z: print(x); print(y); print(z)6 is semantically equivalent to: if x < y < z: print(x); print(y); print(z)7 With more than one item, the context managers are processed as if multiple statements were nested: if x < y < z: print(x); print(y); print(z)8 is semantically equivalent to: if x < y < z: print(x); print(y); print(z)9 You can also write multi-item context managers in multiple lines if the items are surrounded by parentheses. For example: compound_stmt ::=0 Changed in version 3.1: Support for multiple context expressions. Changed in version 3.10: Support for using grouping parentheses to break the statement in multiple lines. See also PEP 343 - The “with” statementThe specification, background, and examples for the Python statement. 8.6. The if x < y < z: print(x); print(y); print(z) 89 statementNew in version 3.10. The match statement is used for pattern matching. Syntax: compound_stmt ::=1 Note This section uses single quotes to denote . Pattern matching takes a pattern as input (following if x < y < z: print(x); print(y); print(z)90) and a subject value (following if x < y < z: print(x); print(y); print(z)89). The pattern (which may contain subpatterns) is matched against the subject value. The outcomes are:
The if x < y < z: print(x); print(y); print(z)89 and if x < y < z: print(x); print(y); print(z)90 keywords are . See also
8.6.1. OverviewHere’s an overview of the logical flow of a match statement:
Note Users should generally never rely on a pattern being evaluated. Depending on implementation, the interpreter may cache values or use other optimizations which skip repeated evaluations. A sample match statement: compound_stmt ::=2 In this case, if x < y < z: print(x); print(y); print(z)99 is a guard. Read more about that in the next section. 8.6.2. Guardscompound_stmt ::=3 A compound_stmt ::=00 (which is part of the if x < y < z: print(x); print(y); print(z)90) must succeed for code inside the if x < y < z: print(x); print(y); print(z)90 block to execute. It takes the form: followed by an expression. The logical flow of a if x < y < z: print(x); print(y); print(z)90 block with a compound_stmt ::=00 follows:
Guards are allowed to have side effects as they are expressions. Guard evaluation must proceed from the first to the last case block, one at a time, skipping case blocks whose pattern(s) don’t all succeed. (I.e., guard evaluation must happen in order.) Guard evaluation must stop once a case block is selected. 8.6.3. Irrefutable Case BlocksAn irrefutable case block is a match-all case block. A match statement may have at most one irrefutable case block, and it must be last. A case block is considered irrefutable if it has no guard and its pattern is irrefutable. A pattern is considered irrefutable if we can prove from its syntax alone that it will always succeed. Only the following patterns are irrefutable:
8.6.4. PatternsNote This section uses grammar notations beyond standard EBNF:
The top-level syntax for compound_stmt ::=16 is: compound_stmt ::=4 The descriptions below will include a description “in simple terms” of what a pattern does for illustration purposes (credits to Raymond Hettinger for a document that inspired most of the descriptions). Note that these descriptions are purely for illustration purposes and may not reflect the underlying implementation. Furthermore, they do not cover all valid forms. 8.6.4.1. OR PatternsAn OR pattern is two or more patterns separated by vertical bars compound_stmt ::=17. Syntax: compound_stmt ::=5 Only the final subpattern may be , and each subpattern must bind the same set of names to avoid ambiguity. An OR pattern matches each of its subpatterns in turn to the subject value, until one succeeds. The OR pattern is then considered successful. Otherwise, if none of the subpatterns succeed, the OR pattern fails. In simple terms, compound_stmt ::=18 will try to match compound_stmt ::=19, if it fails it will try to match compound_stmt ::=20, succeeding immediately if any succeeds, failing otherwise. 8.6.4.2. AS PatternsAn AS pattern matches an OR pattern on the left of the keyword against a subject. Syntax: compound_stmt ::=6 If the OR pattern fails, the AS pattern fails. Otherwise, the AS pattern binds the subject to the name on the right of the as keyword and succeeds. compound_stmt ::=22 cannot be a a compound_stmt ::=23. In simple terms compound_stmt ::=24 will match with compound_stmt ::=25, and on success it will set compound_stmt ::=26. 8.6.4.3. Literal PatternsA literal pattern corresponds to most in Python. Syntax: compound_stmt ::=7 The rule compound_stmt ::=27 and the token compound_stmt ::=28 are defined in the standard Python grammar. Triple-quoted strings are supported. Raw strings and byte strings are supported. are not supported. The forms compound_stmt ::=29 and compound_stmt ::=30 are for expressing ; they require a real number on the left and an imaginary number on the right. E.g. compound_stmt ::=31. In simple terms, compound_stmt ::=32 will succeed only if compound_stmt ::=33. For the singletons if x < y < z: print(x); print(y); print(z)83, compound_stmt ::=35 and compound_stmt ::=36, the operator is used. 8.6.4.4. Capture PatternsA capture pattern binds the subject value to a name. Syntax: compound_stmt ::=8 A single underscore compound_stmt ::=23 is not a capture pattern (this is what compound_stmt ::=39 expresses). It is instead treated as a . In a given pattern, a given name can only be bound once. E.g. compound_stmt ::=41 is invalid while compound_stmt ::=42 is allowed. Capture patterns always succeed. The binding follows scoping rules established by the assignment expression operator in PEP 572; the name becomes a local variable in the closest containing function scope unless there’s an applicable or statement. In simple terms compound_stmt ::=45 will always succeed and it will set compound_stmt ::=26. 8.6.4.5. Wildcard PatternsA wildcard pattern always succeeds (matches anything) and binds no name. Syntax: compound_stmt ::=9 compound_stmt ::=23 is a within any pattern, but only within patterns. It is an identifier, as usual, even within if x < y < z: print(x); print(y); print(z)89 subject expressions, compound_stmt ::=00s, and if x < y < z: print(x); print(y); print(z)90 blocks. In simple terms, compound_stmt ::=23 will always succeed. 8.6.4.6. Value PatternsA value pattern represents a named value in Python. Syntax: if_stmt ::= "if"0 The dotted name in the pattern is looked up using standard Python . The pattern succeeds if the value found compares equal to the subject value (using the compound_stmt ::=52 equality operator). In simple terms compound_stmt ::=53 will succeed only if compound_stmt ::=54 Note If the same value occurs multiple times in the same match statement, the interpreter may cache the first value found and reuse it rather than repeat the same lookup. This cache is strictly tied to a given execution of a given match statement. 8.6.4.7. Group PatternsA group pattern allows users to add parentheses around patterns to emphasize the intended grouping. Otherwise, it has no additional syntax. Syntax: if_stmt ::= "if"1 In simple terms compound_stmt ::=55 has the same effect as compound_stmt ::=25. 8.6.4.8. Sequence PatternsA sequence pattern contains several subpatterns to be matched against sequence elements. The syntax is similar to the unpacking of a list or tuple. if_stmt ::= "if"2 There is no difference if parentheses or square brackets are used for sequence patterns (i.e. compound_stmt ::=57 vs compound_stmt ::=58 ). Note A single pattern enclosed in parentheses without a trailing comma (e.g. compound_stmt ::=59) is a . While a single pattern enclosed in square brackets (e.g. compound_stmt ::=60) is still a sequence pattern. At most one star subpattern may be in a sequence pattern. The star subpattern may occur in any position. If no star subpattern is present, the sequence pattern is a fixed-length sequence pattern; otherwise it is a variable-length sequence pattern. The following is the logical flow for matching a sequence pattern against a subject value:
In simple terms compound_stmt ::=66 … compound_stmt ::=67 matches only if all the following happens:
8.6.4.9. Mapping PatternsA mapping pattern contains one or more key-value patterns. The syntax is similar to the construction of a dictionary. Syntax: if_stmt ::= "if"3 At most one double star pattern may be in a mapping pattern. The double star pattern must be the last subpattern in the mapping pattern. Duplicate keys in mapping patterns are disallowed. Duplicate literal keys will raise a . Two keys that otherwise have the same value will raise a at runtime. The following is the logical flow for matching a mapping pattern against a subject value:
Note Key-value pairs are matched using the two-argument form of the mapping subject’s compound_stmt ::=78 method. Matched key-value pairs must already be present in the mapping, and not created on-the-fly via compound_stmt ::=79 or compound_stmt ::=80. In simple terms compound_stmt ::=81 matches only if all the following happens:
8.6.4.10. Class PatternsA class pattern represents a class and its positional and keyword arguments (if any). Syntax: if_stmt ::= "if"4 The same keyword should not be repeated in class patterns. The following is the logical flow for matching a class pattern against a subject value:
In simple terms if_stmt ::= "if"18 matches only if the following happens:
See also
8.7. Function definitionsA function definition defines a user-defined function object (see section ): if_stmt ::= "if"5 A function definition is an executable statement. Its execution binds the function name in the current local namespace to a function object (a wrapper around the executable code for the function). This function object contains a reference to the current global namespace as the global namespace to be used when the function is called. The function definition does not execute the function body; this gets executed only when the function is called. A function definition may be wrapped by one or more expressions. Decorator expressions are evaluated when the function is defined, in the scope that contains the function definition. The result must be a callable, which is invoked with the function object as the only argument. The returned value is bound to the function name instead of the function object. Multiple decorators are applied in nested fashion. For example, the following code if_stmt ::= "if"6 is roughly equivalent to if_stmt ::= "if"7 except that the original function is not temporarily bound to the name if_stmt ::= "if"26. Changed in version 3.9: Functions may be decorated with any valid . Previously, the grammar was much more restrictive; see PEP 614 for details. When one or more have the form parameter if_stmt ::= "if"28 expression, the function is said to have “default parameter values.” For a parameter with a default value, the corresponding may be omitted from a call, in which case the parameter’s default value is substituted. If a parameter has a default value, all following parameters up until the “ if_stmt ::= "if"29” must also have a default value — this is a syntactic restriction that is not expressed by the grammar. Default parameter values are evaluated from left to right when the function definition is executed. This means that the expression is evaluated once, when the function is defined, and that the same “pre-computed” value is used for each call. This is especially important to understand when a default parameter value is a mutable object, such as a list or a dictionary: if the function modifies the object (e.g. by appending an item to a list), the default parameter value is in effect modified. This is generally not what was intended. A way around this is to use if x < y < z: print(x); print(y); print(z)83 as the default, and explicitly test for it in the body of the function, e.g.: if_stmt ::= "if"8 Function call semantics are described in more detail in section . A function call always assigns values to all parameters mentioned in the parameter list, either from positional arguments, from keyword arguments, or from default values. If the form “ if_stmt ::= "if"31” is present, it is initialized to a tuple receiving any excess positional parameters, defaulting to the empty tuple. If the form “ if_stmt ::= "if"32” is present, it is initialized to a new ordered mapping receiving any excess keyword arguments, defaulting to a new empty mapping of the same type. Parameters after “ if_stmt ::= "if"29” or “ if_stmt ::= "if"31” are keyword-only parameters and may only be passed by keyword arguments. Parameters before “ if_stmt ::= "if"35” are positional-only parameters and may only be passed by positional arguments. Changed in version 3.8: The if_stmt ::= "if"35 function parameter syntax may be used to indicate positional-only parameters. See PEP 570 for details. Parameters may have an of the form “ if_stmt ::= "if"37” following the parameter name. Any parameter may have an annotation, even those of the form if_stmt ::= "if"31 or if_stmt ::= "if"32. Functions may have “return” annotation of the form “ if_stmt ::= "if"40” after the parameter list. These annotations can be any valid Python expression. The presence of annotations does not change the semantics of a function. The annotation values are available as values of a dictionary keyed by the parameters’ names in the if_stmt ::= "if"41 attribute of the function object. If the if_stmt ::= "if"42 import from is used, annotations are preserved as strings at runtime which enables postponed evaluation. Otherwise, they are evaluated when the function definition is executed. In this case annotations may be evaluated in a different order than they appear in the source code. It is also possible to create anonymous functions (functions not bound to a name), for immediate use in expressions. This uses lambda expressions, described in section . Note that the lambda expression is merely a shorthand for a simplified function definition; a function defined in a “” statement can be passed around or assigned to another name just like a function defined by a lambda expression. The “ if_stmt ::= "if"44” form is actually more powerful since it allows the execution of multiple statements and annotations. Programmer’s note: Functions are first-class objects. A “ if_stmt ::= "if"44” statement executed inside a function definition defines a local function that can be returned or passed around. Free variables used in the nested function can access the local variables of the function containing the def. See section for details. See also PEP 3107 - Function AnnotationsThe original specification for function annotations. PEP 484 - Type HintsDefinition of a standard meaning for annotations: type hints. PEP 526 - Syntax for Variable AnnotationsAbility to type hint variable declarations, including class variables and instance variables PEP 563 - Postponed Evaluation of AnnotationsSupport for forward references within annotations by preserving annotations in a string form at runtime instead of eager evaluation. 8.8. Class definitionsA class definition defines a class object (see section ): if_stmt ::= "if"9 A class definition is an executable statement. The inheritance list usually gives a list of base classes (see for more advanced uses), so each item in the list should evaluate to a class object which allows subclassing. Classes without an inheritance list inherit, by default, from the base class ; hence, while_stmt ::= "while"0 is equivalent to while_stmt ::= "while"1 The class’s suite is then executed in a new execution frame (see ), using a newly created local namespace and the original global namespace. (Usually, the suite contains mostly function definitions.) When the class’s suite finishes execution, its execution frame is discarded but its local namespace is saved. A class object is then created using the inheritance list for the base classes and the saved local namespace for the attribute dictionary. The class name is bound to this class object in the original local namespace. The order in which attributes are defined in the class body is preserved in the new class’s if_stmt ::= "if"48. Note that this is reliable only right after the class is created and only for classes that were defined using the definition syntax. Class creation can be customized heavily using . Classes can also be decorated: just like when decorating functions, while_stmt ::= "while"2 is roughly equivalent to while_stmt ::= "while"3 The evaluation rules for the decorator expressions are the same as for function decorators. The result is then bound to the class name. Changed in version 3.9: Classes may be decorated with any valid . Previously, the grammar was much more restrictive; see PEP 614 for details. Programmer’s note: Variables defined in the class definition are class attributes; they are shared by instances. Instance attributes can be set in a method with if_stmt ::= "if"50. Both class and instance attributes are accessible through the notation “ if_stmt ::= "if"51”, and an instance attribute hides a class attribute with the same name when accessed in this way. Class attributes can be used as defaults for instance attributes, but using mutable values there can lead to unexpected results. can be used to create instance variables with different implementation details. See also PEP 3115 - Metaclasses in Python 3000The proposal that changed the declaration of metaclasses to the current syntax, and the semantics for how classes with metaclasses are constructed. PEP 3129 - Class DecoratorsThe proposal that added class decorators. Function and method decorators were introduced in PEP 318. 8.9. CoroutinesNew in version 3.5. 8.9.1. Coroutine function definitionwhile_stmt ::= "while"4 Execution of Python coroutines can be suspended and resumed at many points (see ). expressions, and can only be used in the body of a coroutine function. Functions defined with if_stmt ::= "if"55 syntax are always coroutine functions, even if they do not contain if_stmt ::= "if"52 or if_stmt ::= "if"57 keywords. It is a to use a if_stmt ::= "if"59 expression inside the body of a coroutine function. An example of a coroutine function: while_stmt ::= "while"5 Changed in version 3.7: if_stmt ::= "if"52 and if_stmt ::= "if"57 are now keywords; previously they were only treated as such inside the body of a coroutine function. 8.9.2. The if_stmt ::= "if" assignment_expression ":" suite ("elif" assignment_expression ":" suite)* ["else" ":" suite] 53 statementwhile_stmt ::= "while"6 An provides an if_stmt ::= "if"63 method that directly returns an , which can call asynchronous code in its if_stmt ::= "if"64 method. The if_stmt ::= "if"53 statement allows convenient iteration over asynchronous iterables. The following code: while_stmt ::= "while"7 Is semantically equivalent to: while_stmt ::= "while"8 See also and for details. It is a to use an if_stmt ::= "if"53 statement outside the body of a coroutine function. 8.9.3. The if_stmt ::= "if" assignment_expression ":" suite ("elif" assignment_expression ":" suite)* ["else" ":" suite] 54 statementwhile_stmt ::= "while"9 An is a that is able to suspend execution in its enter and exit methods. The following code: for_stmt ::= "for"0 is semantically equivalent to: for_stmt ::= "for"1 See also and for details. It is a to use an if_stmt ::= "if"54 statement outside the body of a coroutine function. See also PEP 492 - Coroutines with async and await syntaxThe proposal that made coroutines a proper standalone concept in Python, and added supporting syntax. Footnotes The exception is propagated to the invocation stack unless there is a clause which happens to raise another exception. That new exception causes the old one to be lost. In pattern matching, a sequence is defined as one of the following:
The following standard library classes are sequences: Note Subject values of type compound_stmt ::=61, compound_stmt ::=62, and compound_stmt ::=63 do not match sequence patterns. In pattern matching, a mapping is defined as one of the following:
The standard library classes and are mappings. A string literal appearing as the first statement in the class body is transformed into the namespace’s if_stmt ::= "if"93 item and therefore the class’s . |
For each of the following statements, state whether or not the instruction is valid
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