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--- notes:python_cheat_sheet [2026/07/30 16:09]
66.249.64.128 old revision restored (2026/07/29 09:26)
+++ notes:python_cheat_sheet [2026/08/01 12:05] (current)
114.119.158.118 old revision restored (2026/05/19 02:35)
@@ Line 1: / Line 1: @@
 ====== Python Cheat Sheet ======
-===== 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]].
+  * **python**/**python3.1** is the command-line interpreter with readline where available.
-[[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 -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 24: @@
   * 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 47: / Line 41: @@
   * Other sequence types include tuples ( (1,2) or 1,2) and sets ({1,2} or set(1,2)).
-===== Strings =====
+===== Input/Output =====
   * Strings can be enclosed with double or single-quotes.
   * \ in a string by itself goes to the next line but does not insert a newline (\n does).
@@ Line 54: / Line 48: @@
   * 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.
+  * //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.
+  * str() returns a readable representation, repr() returns a canonical representation of any object.
+  * 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.
 ===== Control Flow =====
@@ Line 81: / Line 82: @@
   * 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 99: / Line 100: @@
   * . is the current package, .. is the parent package etc.
-===== Input/Output =====
+===== 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>
-  * 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 load and dump methods for serializing objects. Support should be added for new object types.

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