An Introduction to Python and Computer Programming by Yue Zhang

Author:Yue Zhang
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

6.3 Identifier Scopes

Identifier scope refers to the accessibility of identifiers in different parts of Python code; it is an important concept related to functions. For a simple example of the concept of scopes, consider the accessibility of identifiers from a function body. Statements defined in a function can contain references to identifiers defined outside the function:

In the example above, the identifier math is defined by an import statement outside the function f, but the function body of f contains a direct reference to math. When the function call f(1) is evaluated, the math module object is accessed by the function body successfully, yielding the return value .

Global scope and local scope. Top-level statements in IDLE or a Python program being executed form the global scope, while statements inside a function body being executed form a local scope. Correspondingly, parameters (e.g. x in the example above) and identifiers defined inside functions (e.g. the variable y in the example above) are called local identifiers. Python allows global identifiers to be accessed by local statements, but not vice versa.

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