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notes:python_cheat_sheet [2026/06/07 07:41]
190.7.114.120 old revision restored (2026/05/27 07:05) 		notes:python_cheat_sheet [2026/06/07 13:59] (current)
150.5.134.52 old revision restored (2026/06/03 02:44)
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 ===== Overview ===== ===== Overview =====
  
-[[http://www.python.org/ | Python]] is a dynamic object-oriented programming language with extensive standard libraries. These notes summarize the [[http://docs.python.org/3.1/tutorial/ | Python 3.1 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]]. 
-  * **python**/**python3.1** is the command-line interpreter with readline where available.+ 
 +===== The Interpreter ===== 
 + 
 +  * **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.
-  * %%>>> prompts for a line . ... prompts for a continuation of a previous line.%%+  * 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
   * 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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   * lambda x: x + n creates a small anonymous function.   * lambda x: x + n creates a small anonymous function.
   * A function should contain a triply quoted doc string at the start. This is accessible with func.__doc__ .   * A function should contain a triply quoted doc string at the start. This is accessible with func.__doc__ .
-  * 4 spaces per indent, no tabs. CamelCase for classes lower_case with underscores for functions.+  * 4 spaces per indent, no tabs. CamelCasel for classes lower_case_with_underscores for functions.
  
 ===== Lists ===== ===== Lists =====
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   * A string can be treated as a list of letters.   * A string can be treated as a list of letters.
   * But strings can't be modified using slices or indexes.   * But strings can't be modified using slices or indexes.
-  * [[http://docs.python.org/3.1/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.
  
 ===== Control Flow ===== ===== Control Flow =====
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   * Dictionaries are unordered sets of key value pairs e.g. { a:1, b:2} or dict([(a,1),(b,2)]) or dict(a=1,b=2)   * Dictionaries are unordered sets of key value pairs e.g. { a:1, b:2} or dict([(a,1),(b,2)]) or dict(a=1,b=2)
   * Dictionary keys/values/items can be enumerated over.   * Dictionary keys/values/items can be enumerated over.
-  * sorted and reversed take in lists and return new lists.+  * sorted and reversed take in liats and return new lists.
   * enumerate takes in a list and returns a list of pairs where the first item in the pair is an integer starting with 0.   * enumerate takes in a list and returns a list of pairs where the first item in the pair is an integer starting with 0.
   * 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.
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 from fib import fib1, fib2 from fib import fib1, fib2
 </code> </code>
-  * %%__name__%% is set to the name of the module or to %%__main__%% if called from the command line.+  * <code python>__name__</code> is set to the name of the module or to <code python>__main__</code> 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.   * 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.   * When a module is imported, a byte-code version is stored to module.pyc which speeds up successive loads.
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   * str() returns a readable representations, repr() returns a canonical representation   * str() returns a readable representations, repr() returns a canonical representation
   * Strings have several formatting methods.    * Strings have several formatting methods. 
-  * //formatstring.format(tuple)// is the [[http://docs.python.org/3.1/library/string.html#formatspec | new-style printf]] equivalent. The [[http://docs.python.org/3.1/library/stdtypes.html#old-string-formatting | old-style]] was //formatstring % (tuple)// which uses C-type format strings.+  * [[ http://docs.python.org/3.0/library/string.html#formatspec | formatstring.format(tuple)]] is the printf equivalent. The old style was [[http://docs.python.org/3.0/library/stdtypes.html#old-string-formatting | formatstring % (tuple)]] which uses C-type format strings.
   * To open a file <code python> open('/tmp/workfile', 'w') </code>   * To open a file <code python> open('/tmp/workfile', 'w') </code>
-  * [[http://docs.python.org/3.1/library/stdtypes.html#file-objects | File methods]] include read, readline, write. +  * File methods include read, readline, write. 
-  * //pickle// contains [[http://docs.python.org/3.1/library/pickle.html | load and dump methods]] for serializing objects. Support should be added for new object types. +  * //pickle// contains load and dump methods for serializing objects. Support should be added for new object types.
- +
-===== Error Handling ===== +
- +
-  * Syntax errors are parsing errors, exceptions are runtime errors. +
-  * Exceptions are class objects in the exceptions module. [[http://docs.python.org/3.1/library/exceptions.html#bltin-exceptions | List of builtin exceptions]]. +
-  * Exception handling is supported using try..except..else..finally :<code python> +
-try: +
-    result = x / y +
-except ZeroDivisionError: +
-    print("division by zero!") +
-except Exception as inst: +
-    print(type(inst))    # the exception instance +
-    print(inst.args)     # arguments stored in .args +
-    print(inst)          # also prints .args +
-else: +
-    print("result is", result) +
-finally: +
-    print("executing finally clause") +
-</code> +
-  * Errors can be raised using ''raise Exception('mine')'' or just ''raise'' in an exception handler. +
-  * New exception classes can be created and should derive from the Exception class. +
-  * ''with'' can be used to automatically call the cleanup actions of an object e.g. <code python> +
-with open("myfile.txt") as f: +
-    for line in f: +
-        print(line) +
-</code> +
notes/python_cheat_sheet.1780843281.txt.gz · Last modified: 2026/06/07 07:41 by 190.7.114.120

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