# Tutorial by Examples

## Accessing list values

Python lists are zero-indexed, and act like arrays in other languages. lst = [1, 2, 3, 4] lst[0] # 1 lst[1] # 2 Attempting to access an index outside the bounds of the list will raise an IndexError. lst[4] # IndexError: list index out of range Negative indices are interpreted as countin...

## List methods and supported operators

Starting with a given list a: a = [1, 2, 3, 4, 5] append(value) – appends a new element to the end of the list. # Append values 6, 7, and 7 to the list a.append(6) a.append(7) a.append(7) # a: [1, 2, 3, 4, 5, 6, 7, 7] # Append another list b = [8, 9] a.append(b) # a: [1, 2, 3, 4, ...

## Length of a list

Use len() to get the one-dimensional length of a list. len(['one', 'two']) # returns 2 len(['one', [2, 3], 'four']) # returns 3, not 4 len() also works on strings, dictionaries, and other data structures similar to lists. Note that len() is a built-in function, not a method of a list objec...

## Iterating over a list

Python supports using a for loop directly on a list: my_list = ['foo', 'bar', 'baz'] for item in my_list: print(item) # Output: foo # Output: bar # Output: baz You can also get the position of each item at the same time: for (index, item) in enumerate(my_list): print('The item i...

## Checking whether an item is in a list

Python makes it very simple to check whether an item is in a list. Simply use the in operator. lst = ['test', 'twest', 'tweast', 'treast'] 'test' in lst # Out: True 'toast' in lst # Out: False Note: the in operator on sets is asymptotically faster than on lists. If you need to use it ...

## Reversing list elements

You can use the reversed function which returns an iterator to the reversed list: In [3]: rev = reversed(numbers) In [4]: rev Out[4]: [9, 8, 7, 6, 5, 4, 3, 2, 1] Note that the list &quot;numbers&quot; remains unchanged by this operation, and remains in the same order it was originally. To r...

## Checking if list is empty

The emptiness of a list is associated to the boolean False, so you don't have to check len(lst) == 0, but just lst or not lst lst = [] if not lst: print(&quot;list is empty&quot;) # Output: list is empty

## Concatenate and Merge lists

The simplest way to concatenate list1 and list2: merged = list1 + list2 zip returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables: alist = ['a1', 'a2', 'a3'] blist = ['b1', 'b2', 'b3'] for a, b in zip(alist, blist):...

## Any and All

You can use all() to determine if all the values in an iterable evaluate to True nums = [1, 1, 0, 1] all(nums) # False chars = ['a', 'b', 'c', 'd'] all(chars) # True Likewise, any() determines if one or more values in an iterable evaluate to True nums = [1, 1, 0, 1] any(nums) # True val...

## Remove duplicate values in list

Removing duplicate values in a list can be done by converting the list to a set (that is an unordered collection of distinct objects). If a list data structure is needed, then the set can be converted back to a list using the function list(): names = [&quot;aixk&quot;, &quot;duke&quot;, &quot;edik&...

## Accessing values in nested list

Starting with a three-dimensional list: alist = [[[1,2],[3,4]], [[5,6,7],[8,9,10], [12, 13, 14]]] Accessing items in the list: print(alist[0][0][1]) #2 #Accesses second element in the first list in the first list print(alist[1][1][2]) #10 #Accesses the third element in the second list in...

## Comparison of lists

It's possible to compare lists and other sequences lexicographically using comparison operators. Both operands must be of the same type. [1, 10, 100] &lt; [2, 10, 100] # True, because 1 &lt; 2 [1, 10, 100] &lt; [1, 10, 100] # False, because the lists are equal [1, 10, 100] &lt;= [1, 10, 100] #...

## Initializing a List to a Fixed Number of Elements

For immutable elements (e.g. None, string literals etc.): my_list = [None] * 10 my_list = ['test'] * 10 For mutable elements, the same construct will result in all elements of the list referring to the same object, for example, for a set: &gt;&gt;&gt; my_list=[{1}] * 10 &gt;&gt;&gt; print(my_...

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