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Python Modules

Python Modules. Modules in a Nutshell. Modules are text files you can import to the Python interpreter in order to reuse previously written code. A module has its own global and local scopes to prevent interference with user defined names.

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Python Modules

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  1. Python Modules

  2. Modules in a Nutshell • Modules are text files you can import to the Python interpreter in order to reuse previously written code. • A module has its own global and local scopes to prevent interference with user defined names. • A package is a collection of modules, grouped for organization and easy access.

  3. Module Example $ vim mymodule.py # a simple module def square(x): “”” Returns the square of its parameter. “”” return x * x

  4. Using a module >>> import mymodule >>> y = mymodule.square(2) >>>y 4 >>>mymodule.square(y) 16

  5. Call by Value >>> import mymodule >>> x = 7 >>> mymodule.square(x) 49 >>> x 7

  6. Accessing the module variables • You can access the global variables of a module using dot notation. >>> x = somemodule.somevariable • Global variables in a module will not otherwise effect another module, or user defined components.

  7. from/import Statements • You can import specific names from a module with a from/import statement. >>> from mymodule import square >>> square(3) 9 >>> from mymodule import square, cube >>> cube(2) 8 >>> from mymodule import *

  8. The Importance of Returning • Python modules don’t really handle function calls by reference. Programmers have to work around this with return statements. >>> x = 2 >>> x = mymodule.square(2) >>> x 4

  9. Modules as Scripts $ vim mymodule.py def square(x): print x * x if __name__ == "__main__": import sys square(int(sys.argv[1])) ~ ~ $ python mymodule.py 2 4

  10. .pyc Files • On a successful import, a modulename.pyc file is generated. This file contains the bytecode from the last time the modulename.py file was imported. • The interpreter checks the date modified before using the .pyc file, there is no danger of using an older version. • These files only speed up the loading of a module, not the execution.

  11. dir() • dir() is useful for checking what modules you’ve imported. >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import mymodule >>> from mymodule import square >>> dir() ['__builtins__', '__doc__', '__name__', '__package__', 'mymodule', 'square']

  12. Standard Modules • import first checks the current directory for the specified module. • The interpreter then follows a default path like /usr/local/lib/python, or the PYTHONPATH EV. • To change the path, import “sys”, one of Python’s standard modules. >>> import sys >>> sys.path.append(‘/home/jm4564/cs_265’)

  13. A Package Example math/ __init__.py logarithms.py circles.py statistics/ factorial.py … …

  14. Importing Packages • Packages can be imported in as large, or as small, portions as you require. >>> import math.circles >>> math.circles.area(5) 78.53981634 >>> from math.circles import area >>> area(3) 28.27433388

  15. Questions?

  16. Source • Python v2.6.4 documentation >> The Python Tutorial >> Modules http://docs.python.org/tutorial/modules.html

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