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notes:python_cheat_sheet [2026/06/11 19:23]
114.119.135.121 old revision restored (2026/06/02 16:30) 		notes:python_cheat_sheet [2026/06/13 18:52] (current)
216.73.216.147 old revision restored (2026/06/13 16:14)
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 [[http://www.python.org/ | Python]] is a dynamic object-oriented programming language with extensive standard libraries. These notes summarize the [[http://docs.python.org/3.0/tutorial/ | Python 3.0 tutorial]]. [[http://www.python.org/ | Python]] is a dynamic object-oriented programming language with extensive standard libraries. These notes summarize the [[http://docs.python.org/3.0/tutorial/ | Python 3.0 tutorial]].
- 
-===== The Interpreter ===== 
- 
   * **python**/**python3.0** is the command-line interpreter with readline where available.   * **python**/**python3.0** is the command-line interpreter with readline where available.
   * python -c command runs a single command.   * python -c command runs a single command.
-  * sys.argv is a list of strings with the script if any in sys.argv[0] +  * %%>>> prompts for a line . ... prompts for a continuation of a previous line.%%
-  * >>> prompts for a line . ... prompts for a continuation of a previous line+
   * PYTHONSTARTUP can point to a file of startup commands   * PYTHONSTARTUP can point to a file of startup commands
   * Expressions are evaluated and printed.   * Expressions are evaluated and printed.
   * The last printed expression is assigned to _ .   * The last printed expression is assigned to _ .
- 
  
 ===== Basics ===== ===== Basics =====
   * Comments start with # .   * Comments start with # .
 +  * sys.argv is a list of strings with the script if any in sys.argv[0]
   * Variables can be assigned (using = ) without being defined but must be assigned before being used.   * Variables can be assigned (using = ) without being defined but must be assigned before being used.
   * a,b = c,d does a multiple assignment.   * a,b = c,d does a multiple assignment.
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   * Lists can be nested.   * Lists can be nested.
   * Other methods include append, pop, extend, index, count, sort, reverse.   * Other methods include append, pop, extend, index, count, sort, reverse.
-  * Lists can be created from sequences e.g <code python>+  * Lists can be created from sequences using list comprehension <code python>
 vec = [2, 4, 6] vec = [2, 4, 6]
-[[x, x**2] for x in vec] +[[x, x**2] for x in vec if x > 2] 
-[[2, 4], [4, 16], [6, 36]]</code>+[[4, 16], [6, 36]] 
 +[x+y for x in vec for y in vec2 if x > 2]</code>
   * Other sequence types include tuples ( (1,2) or 1,2) and sets ({1,2} or set(1,2)).   * Other sequence types include tuples ( (1,2) or 1,2) and sets ({1,2} or set(1,2)).
  
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   * But strings can't be modified using slices or indexes.   * But strings can't be modified using slices or indexes.
   * [[http://docs.python.org/3.0/library/stdtypes.html#string-methods | String methods]] include strip, format, capitalize etc.   * [[http://docs.python.org/3.0/library/stdtypes.html#string-methods | String methods]] include strip, format, capitalize etc.
-  * format-string % (tuple) allows use of printf formatting strings. Also string.format() . 
  
 ===== Control Flow ===== ===== Control Flow =====
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   * zip takes two or more lists with the same number of elements and creates a single list of lists with corresponding members grouped together.   * zip takes two or more lists with the same number of elements and creates a single list of lists with corresponding members grouped together.
  
-===== Modules =====+===== Modules & Packages ===== 
 + 
 +  * A //module// is a file of python definitions. 
 +  * Definitions in a module can be accessed by importing the module. <code python>import fib 
 +from fib import fib1, fib2 
 +</code> 
 +  * %%__name__%% is set to the name of the module or to %%__main__%% if called from the command line. 
 +  * The search list for modules is the variable sys.path initialized from the directory containing the input script (or the current directory), PYTHONPATH and the installation-dependent default. 
 +  * When a module is imported, a byte-code version is stored to module.pyc which speeds up successive loads. 
 +  * There are many standard modules including sys which is common to all platforms. 
 +  * dir(module) lists all names in a module sorted alphabetically. dir(builtins) shows all the built-in functions and variables. 
 +  * Packages can be used to group modules. Packages should be in a named directory with an __init__.py file optionally containing initialization code. E.g. import sound.effects.echo . 
 +  * . is the current package, .. is the parent package etc. 
 + 
 +===== Input/Output ===== 
 + 
 +  * str() returns a readable representations, repr() returns a canonical representation 
 +  * Strings have several formatting methods.  
 +  * //formatstring.format(tuple)// is the [[http://docs.python.org/3.0/library/string.html#formatspec | new-style printf]] equivalent. The [[http://docs.python.org/3.0/library/stdtypes.html#old-string-formatting | old-style]] was //formatstring % (tuple)// which uses C-type format strings. 
 +  * To open a file <code python> open('/tmp/workfile', 'w') </code> 
 +  * [[http://docs.python.org/3.0/library/stdtypes.html#file-objects | File methods]] include read, readline, write. 
 +  * //pickle// contains [[http://docs.python.org/3.0/library/pickle.html | load and dump methods]] for serializing objects. Support should be added for new object types.
notes/python_cheat_sheet.1781231033.txt.gz · Last modified: 2026/06/11 19:23 by 114.119.135.121

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