Differences

This shows you the differences between two versions of the page.

--- notes:python_cheat_sheet [2009/12/18 17:37]
smthng Change to version 3.1
+++ notes:python_cheat_sheet [2009/12/18 18:06] (current)
smthng
@@ 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]].
@@ Line 43: / 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 51: / Line 49: @@
   * 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.
+  * //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 95: / Line 100: @@
   * . is the current package, .. is the parent package etc.
-===== Input/Output =====
+===== Error Handling =====
-  * str() returns a readable representations, repr() returns a canonical representation
+  * Syntax errors are parsing errors, exceptions are runtime errors.
-  * Strings have several formatting methods.
+  * Exceptions are class objects in the exceptions module. [[http://docs.python.org/3.1/library/exceptions.html#bltin-exceptions | List of builtin exceptions]].
-  * //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.
+  * Exception handling is supported using try..except..else..finally :<code python>
-  * To open a file <code python> open('/tmp/workfile', 'w') </code>
+try:
-  * [[http://docs.python.org/3.1/library/stdtypes.html#file-objects | File methods]] include read, readline, write.
+    result = x / y
-  * //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.
+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>
+===== Classes =====