Python Tutorial, Release 3.9.5 42 Chapter 6. Modules 6.1 More on Modules 1 In fact function definitions are also ‘statements’ that are ‘executed’; the execution of a module-level function definition enters the function name in the module’s global symbol table. >>> fib =fibo.fib >>> fib(500 ) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 A module can contain executable statements as well as function definitions. These statements are intended to initialize the module. They are executed only the first time the module name is encountered in an import statement. 1 (They are also run if the file is executed as a script.) Each module has its own private symbol table, which is used as the global symbol table by all functions defined in the module. Thus, the author of a module can use global variables in the module without worrying about accidental clashes with a user’s global variables. On the other hand, if you know what you are doing you can touch a module’s global variables with the same notation used to refer to its functions, modname.itemname . Modules can import other modules. It is customary but not required to place all$_{import}$ statements at the beginning of a module (or script, for that matter). The imported module names are placed in the importing module’s global symbol table. There is a variant of the import statement that imports names from a module directly into the importing module’s symbol table. For example: This does not introduce the module name from which the imports are taken in the local symbol table (so in the example,$_{fibo}$ is not defined). There is even a variant to import all names that a module defines: This imports all names except those beginning with an underscore ($_{_}$). In most cases Python programmers do not use this facility since it introduces an unknown set of names into the interpreter, possibly hiding some things you have already defined. Note that in general the practice of importing$_{*}$from a module or package is frowned upon, since it often causes poorly readable code. However, it is okay to use it to save typing in interactive sessions. If the module name is followed by$_{as}$, then the name following$_{as}$ is bound directly to the imported module. This is effectively importing the module in the same way that$_{import fibo}$ will do, with the only difference of it being available as$_{fib}$. It can also be used when utilising$_{from}$with similar effects: >>> from fibo import fib as fibonacci >>> fibonacci(500 ) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 >>> import fibo as fib >>> fib.fib(500 ) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 >>> from fibo import * >>> fib(500 ) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 >>> from fibo import fib, fib2 >>> fib(500 ) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377