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--- notes:python_cheat_sheet [2026/11/03 00:30]
47.79.201.159 old revision restored (2026/09/11 20:57)
+++ notes:python_cheat_sheet [2026/11/03 03:29] (current)
101.166.17.61 old revision restored (2026/08/03 07:52)
@@ Line 3: / Line 3: @@
 ===== 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/3.0/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/3.1/tutorial/ | Python 3.1 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.
-  * 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
   * Expressions are evaluated and printed.
   * The last printed expression is assigned to _ .
 ===== Basics =====
   * 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.
   * a,b = c,d does a multiple assignment.
@@ Line 30: / Line 26: @@
   * 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__ .
-  * 4 spaces per indent, no tabs. CamelCasel for classes lower_case_with_underscores for functions.
+  * 4 spaces per indent, no tabs. CamelCase for classes lower_case with underscores for functions.
 ===== Lists =====
@@ Line 54: / Line 50: @@
   * A string can be treated as a list of letters.
   * 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/3.1/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 =====
@@ Line 82: / Line 77: @@
   * 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.
-  * sorted and reversed take in liats and return new lists.
+  * sorted and reversed take in lists 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.
   * zip takes two or more lists with the same number of elements and creates a single list of lists with corresponding members grouped together.
@@ Line 92: / Line 87: @@
 from fib import fib1, fib2
 </code>
-  * __name__ is set to the name of the module or to __main__ if called from the command line.
+  * %%__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.
@@ Line 99: / Line 94: @@
   * 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/3.1/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.
+  * 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.
+  * //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.
+===== 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 <code python>raise Exception('mine')</code> or just <code python>raise</code> in an exception handler.
+  *

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