Modules and Packages. CS 339R (Python) Chapter 8

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1 Modules and Packages CS 339R (Python) Chapter 8 Spring 2011

2 Loading a Module The import statement: Reads the source file Creates a module object in the current scope Executes all top-level statements You can put any module initialization code at module scope All top-level definitions become attributes of the module object And are considered global to the module Modules are only imported once per scope Subsequent imports of the same module are ignored 2

3 Renaming Module Objects Use the import as feature Only the local module object takes the new name Handy for selecting the appropriate module at runtime if format == 'xml': import xmlreader as reader elif format == 'csv': import csvreader as reader data = reader.read_data(filename) 3

4 Import Selected Features from <module> import <symbols> The symbols are added to the current scope So you don t have to say <module>.<symbol> Import all symbols with *! (use sparingly) from spam import foo # Imports spam and puts 'foo' in current namespace foo() # Calls spam.foo() from spam import baz as f f(1) # Calls spam.baz(1) from bar import * # all bar s names are now local See mymod.py 4

5 Restricting import * You can choose from within a module what gets imported with an import * Place the desired names to export in a list named all at module scope # module: spam.py # Names I will export with from spam import * all = ['bar', 'Spam'] 5

Don t Forget Scope Rules # In spam.py: a = 37 # spam.a def foo(): print "I'm foo and a is",a # In a client module: from spam import a, foo # Import a global variable a = 42 # Modify main.

6 Don t Forget Scope Rules # In spam.py: a = 37 # spam.a def foo(): print "I'm foo and a is",a # In a client module: from spam import a, foo # Import a global variable a = 42 # Modify main.a only foo() # Prints "I'm foo and a is 37" print a # Prints "42" The global namespace for a function is always the module in which the function was defined, not the namespace into which a function is imported and called. 6

7 The Module Search Path >>> import sys >>> print sys.path ['', '/Library/Frameworks/Python.framework/Versions/2.7/lib/ python27.zip', '/Library/Frameworks/Python.framework/Versions/2.7/ lib/python2.7', '/Library/Frameworks/Python.framework/Versions/2.7/ lib/python2.7/plat-darwin', '/Library/Frameworks/Python.framework/ Versions/2.7/lib/python2.7/plat-mac', '/Library/Frameworks/ Python.framework/Versions/2.7/lib/python2.7/plat-mac/libscriptpackages', '/Library/Frameworks/Python.framework/Versions/ 2.7/lib/python2.7/lib-tk', '/Library/Frameworks/Python.framework/ Versions/2.7/lib/python2.7/lib-old', '/Library/Frameworks/ Python.framework/Versions/2.7/lib/python2.7/lib-dynload', '/ Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ site-packages'] 7

8 Changing the Module Search Path It s just a list You can append to it: sys.path.append( /User/chuck/UVU/mydir ) You can also set the PYTHONPATH environment variable prepends to sys.path 8

9 Searching Zip Files Zip files can also go into the module search path They behave as if they were directories In the example below, the file archive.zip contains the file prod_cons.py (Homework 4) >>> import sys >>> sys.path.append('archive.zip') >>> import prod_cons A BBB EEEEEE F G Z Y W P Q R ABB BEE EEE E F GZY W PQ R >>> dir(prod_cons) [' builtins ', ' doc ', ' file ', ' loader ', ' name ', ' package ', 'consume', 'p', 'produce', 's'] 9

10 Running Modules from the Search Path Use the -m option It finds the module via sys.path, and runs it as the main module dhcp :339r chuck$ python cprofile.py perfect.py /Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python: can't open file 'cprofile.py': [Errno 2] No such file or directory dhcp :339r chuck$ dhcp :339r chuck$ python -m cprofile perfect.py function calls in seconds Ordered by: standard name ncalls tottime percall cumtime percall filename:lineno(function) perfect.py:1(<module>) perfect.py:1(perfect) {method 'disable' of '_lsprof.profiler' objects} {range} {sum} 10

11 Packages Hierarchies of Modules Created by a tree of directories Each directory must have an init.py You can import an intermediate subdirectory import foo.bar Modules foo and foo.bar are created Objects defined in the init.py files are bound to their module objects 11

12 A Sample Package foo # foo/bar/baz.py name = "joe" print 'foo/bar/baz.py' bar bar2 baz.py Each.py file has a trace print statement >>> import foo.bar.baz foo/ init.py foo/bar. init.py foo/bar/baz.py >>> import foo.bar2 foo/bar2/ init.py >>> print foo.bar.baz.name joe 12

13 Package-Relative Imports Allows importing modules in the same package with UNIX-style relative directory syntax (without slashes) from. import lines!!!!! # import child module from..primitive import shape!! # import sibling module Only allowed in packages Only allowed with from... import... style syntax 13

14 Importing An Entire Package You must arrange for each submodule to import its children See foo2 package 14

15 Reminder: about main If a module is loaded at the top level (when launching python), its module name is main You can then test to know whether a module is the top one: if name == main : # Loaded as top-level (perform module test code)... else: # imported from another module (usually do nothing here) 15

16 Packages and main You can have a main module for a package Formed differently than the if name == main method Runs whenever you execute the package from the command-line: python foo python table2 It will load and execute the module in file main.py in the foo directory Ditto for Zip files Beware directory dependencies (may need to alter sys.path or use os.path.chdir) 16

17 Distributing Applications Use the distutils module for typical Python distributions First place your files in a directory Then include a setup.py file there Then call: python setup.py sdist!! # For a source distribution python setup.py bdist!! # For.pyc distribution 17

18 Installing a Distribution Unzip the distribution file Run python setup.py install in the distribution s root directory The module/package is added to your site-packages directory See table2 example 18

Lecture 4. Introduction to Python! Lecture 4

Lecture 4. Introduction to Python! Lecture 4 Lecture 4 Introduction to Python Lecture 4 Summary Modules (general things) Using modules Importing modules Standard Library modules Modules search path Import modules phases Packages Organizing Python