Python defines a long list of special methods to customize class behavior. This is a short list for the Basic Customizations . Method Description object.__new__(cls[, ...]) Called to create a new instance of class cls. __new__() is a static method (special-cased so you need not declare it as such) that takes the class of which an instance was requested as its first argument. __new__() is intended mainly to allow subclasses of immutable types (like int, str, or tuple) to customize instance creation. It is also commonly overridden in custom metaclasses in order to customize class creation. object.__init__(self[,...]) Called when the instance is created. The arguments are those passed to the class constructor expression. If a base class has an __init__() method, the derived class’s __init__()...

Python list comprehension with if-else condition in general: new_list =[ (F, T) [boolean test] for x in old_lis... #!/usr/local/bin/python l = [ 1, 2, 3, 4 ] ...

The sort operation for a Python list sorts a list in place . It takes three optional arguments to control the comparisons: s.sort([cmp[, key[, reverse]]]) cmp specifies a custom comparison function of two arguments (list items) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower()) . The default value is None . key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower . The default value is None . reverse is a boolean value. If set to True , then the list elements are sorted as if each comparison were reversed. Python 2.7 (r27:82525, Jul 4 2010, 09:01:59) [MSC...

Perl uses the pop function to remove an item from the end of an array, and the shift function to remove an item from the beginning of an array. Python does not have a shift function, but its pop function takes a optional parameter. To remove an item from the beginning of a list , simply pop(0) . >>> a = [] >>> a.append(1) >>> a.append(2) ...

Python doesn't seem to have a built-in function to find an object in a list that satisfies a specified criterion, for example, making a function f to return True . To find jack among people : jack = None for p in people: if p.first_... This is not a lot of code, but it's not terse enough as you would expect of Python. Some suggestions are offered here: http://dev.ionous.net/2009/01/python-find-item-in-list.html http://tomayko.com/writings/cleanest-python-find-in-list-function

Python lists are enclosed in square brackets. When a list of objects are enclosed in parentheses it is a tuple (an immutable list). List comprehensions are enclosed in square brackets. But when you change the square brackets to parentheses, you get a generator not a tuple ! >>> l = [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> t = (1,...

# The one liner frequency_dict.keys().sort() d...

Use os.listdir to list the contents of a directory: import os # list the contents of mydir. Cur...

Obtain a slice with the step parameter: new_list = old_list[start:stop:step] >>> a ['a', 1, 'b', 2, 'c', 3] >>> a[::2] ...

Use the built-in dict function: >>> dict([(1,2), (3,4), (5,6)]) {1: 2, 3: 4, 5:... Or, if you have a list with even number of elements and want to use the odd numbered elements for key and even numbered elements for value: >>> a = [ 'a', 1, 'b', 2, 'c', 3 ] >>> dict([(a...