A Python module groups related functions, classes, variables, or other objects under one name. Most modules are Python source files: a file named mymath.py defines a module imported as mymath. Modules make reusable code easier to organize and give it a separate namespace, so mymodule.reverse and othermodule.reverse can coexist. section 10.1 section 10.2
Listing 10.1 File mymath.py
"""mymath - our example math module""" pi = 3.14159 def area(r): """area(r): return the area of a circle with radius r.""" return(pi * r * r)
The small mymath.py file shows a module containing a value, a function, and documentation strings. section 10.2
Import and call a function
With mymath.py available, `import mymath` lets you call `mymath.area(2)`, which returns `12.56636`, or read `mymath.pi`, which is `3.14159`. The import does not make bare `area(2)` or `pi` available. Use `from mymath import pi` if you want to refer to that value without the module prefix. section 10.2
Choose an import form according to how explicitly you want names identified:
- `import modulename` keeps calls qualified, making their origin clear and avoiding clashes with identically named objects in other modules. section 10.3
- `from modulename import name1, name2` makes only those names directly available. section 10.3
- `from modulename import *` imports public names without a prefix. It can overwrite an existing name and obscure where names came from; underscore-prefixed names are normally excluded, while `__all__` can specify what is imported. section 10.3
Python must be able to find the file before it can import the module. Keep a program-specific module beside the program, or put shared modules in a directory included in the module search path, visible through `sys.path`. In Colaboratory, upload the file to the current notebook session or create it there before importing it. section 10.4.1 section 10.1
Editing a module file does not make an existing interactive session use the changes automatically. After editing an imported module, use `importlib.reload(mymath)` to load the revised version. section 10.2
A file can serve as both a module and a runnable script. Put script-only work behind `if __name__ == '__main__':` so importing the file makes its functions available without running its main routine. section 11.1.3
When one module grows too broad, split related responsibilities into modules within a package. A package groups modules in a directory; for example, text-cleaning functions and word-counting functions can live in separate modules while remaining part of one package. section 18.1 section 18.6.2
