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Python Data Structures By Greg Felber

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Lists An ordered group of items Does not need to be the same type Could put numbers, strings or donkeys in the same list List notation A = [1,”This is a list”, c, Donkey(“kong”)]

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Methods of Lists List.append(x) adds an item to the end of the list List.extend(L) Extend the list by appending all in the given list L List.insert(I,x) Inserts an item at index I List.remove(x) Removes the first item from the list whose value is x

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Examples of other methods a = [66.25, 333, 333, 1, 1234.5] //Defines List print a.count(333), a.count(66.25), a.count('x') //calls method 2 1 0 //output a.index(333) //Returns the first index where the given value appears 1 //ouput a.reverse() //Reverses order of list a //Prints list a [333, 1234.5, 1, 333, -1, 66.25] //Ouput a.sort() a //Prints list a [-1, 1, 66.25, 333, 333, 1234.5] //Output

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Using Lists as Stacks The last element added is the first element retrieved To add an item to the stack, append() must be used stack = [3, 4, 5] stack.append(6) Stack is now [3, 4, 5, 6] To retrieve an item from the top of the stack, pop must be used Stack.pop() 6 is output Stack is now [3, 4, 5] again

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Using Lists as Queues First element added is the first element retrieved To do this collections.deque must be implemented

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List Programming Tools Filter(function, sequence) Returns a sequence consisting of the items from the sequence for which function(item) is true Computes primes up to 25

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Map Function Map(function, sequence) Calls function(item) for each of the sequence’s items Computes the cube for the range of 1 to 11

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Reduce Function Reduce(function, sequence) Returns a single value constructed by calling the binary function (function) Computes the sum of the numbers 1 to 10

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The del statement A specific index or range can be deleted

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Tuples Tuple A number of values separated by commas Immutable Cannot assign values to individual items of a tuple However tuples can contain mutable objects such as lists Single items must be defined using a comma Singleton = ‘hello’,

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Sets An unordered collection with no duplicate elements Basket = [‘apple’, ‘orange’, ‘apple’, ‘pear’] Fruit = set(basket) Fruit Set([‘orange’, ‘apple’, ‘pear’])

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Dictionaries Indexed by keys This can be any immutable type (strings, numbers…) Tuples can be used if they contain only immutable objects

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Looping Techniques Iteritems(): for retrieving key and values through a dictionary

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Looping Techniques Enumerate(): for the position index and values in a sequence

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Zip(): for looping over two or more sequences

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Comparisons Operators “in” and “not in” can be used to see if an item exists in a sequence Comparisons can be chained a < b == c This tests whether a is less than b and that b equals c