Download Python: Modules

Juancho Datu
What is a Module?
 File containing Python definitions and statements
with the suffix ‘.py’ in the current directory
 For example file name:
 markov.py

Name becomes the global variable __name__
 Import into Python interpreter with:
 import markov
 Access functions in the module with:
 markov.mca(alice30.txt)
More about Modules
 Global variables in module don’t affect the user’s
global variables
 Module variables can be accessed
 modulename.itemname
 Modules can import other modules
 from markov import *


Placed at the beginning of importing module
* imports all names
Executing as Scripts
 Can run a Python module with:
 python markov.py <arguments>
 Sets ‘__name__’ to ‘__main__’
 if __name__ == "__main__":
 import sys
 markov(str(sys.argv[1]))
 Can be run as a script if above is placed at end of
module
 $ python markov.py alice30.txt
Module Search Path
 Can be modified in Unix
 /usr/local/lib/python
 Can be listed in:
 Environment variable ‘PYTHONPATH’
‘Compiled’ Python Files
 .pyc file created when .py is complied
 ‘byte-compiled’ version of the .py module
 Can optimize code with –O or –OO flag
 Creates .pyo files
 Program doesn’t run faster with .pyc or .pyo
 The modules are just loaded faster
Standard Modules
 Comes with library of standard modules
 ‘sys’ module
 sys.path can be used to modify PYTHONPATH
 >>> import sys
 >>> sys.path.append(‘[Path to be added]')
dir() Function
 Returns sorted list of all the names defined by the
module
 >>> import sys
 >>> dir(sys)
 ['__displayhook__', '__doc__', '__excepthook__', '__name__', '__stderr__', '__stdin__',
'__stdout__', '_getframe', 'api_version', 'argv', 'builtin_module_names', 'byteorder',
'callstats', 'copyright', 'displayhook', 'exc_clear', 'exc_info', 'exc_type', 'excepthook',
'exec_prefix', 'executable', 'exit', 'getdefaultencoding', 'getdlopenflags', 'getrecursionlimit',
'getrefcount', 'hexversion', 'maxint', 'maxunicode', 'meta_path', 'modules', 'path',
'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'setcheckinterval',
'setdlopenflags', 'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', 'version',
'version_info', 'warnoptions']
Packages
 Collection of modules
 __init__.py starts the list of modules in a package
Packages cont.
 Import individual modules
 import sound.effects.echo
 If ‘__init__.py’ includes
 __all__ = ["echo", "surround", "reverse"]
 Then the following statement would import those listed above
 from sound.effects import *
 ‘__path__’ attribute is initialized with the list containing
name of the directory holding package’s ‘__init__.py’
 Can be modified to extend set of modules in a package
Intra-package References
 Sometimes modules in different subpackages need to
reference a module in another subpackage
 If ‘sound.filters.vocoder’ module needed to use ‘echo’
in the ‘sound.effects’ package:
 from sound.effects import echo
 Can also use implicit relative imports
 from . import echo
 from ..filters import equalizer
Questions?