Python Container Types and Handy Tricks for Lists, Dictionaries, and More

Python provides a rich set of container data types, including list , tuple , set , and dict . Below are several useful tricks to write more Pythonic code.

Extract maximum value from a dictionary

<code>max(my_dict.values())</code>

Get the key of the maximum value:

<code>max(my_dict, key=my_dict.get)</code>

Get both the key and value of the maximum entry:

<code>max(my_dict.items(), key=lambda x: x[1])</code>

Alternative using operator.itemgetter :

<code>import operator
max(my_dict.items(), key=operator.itemgetter(1))</code>

Count occurrences of each element in a list

<code>{x: my_list.count(x) for x in set(my_list)}</code>

Or using itertools.groupby :

<code>from itertools import groupby
{key: len(list(group)) for key, group in groupby(sorted(my_list))}</code>

Or using collections.Counter :

<code>from collections import Counter
dict(Counter(my_list))</code>

Truncate a list efficiently

<code>my_list = my_list[:i]
my_list = my_list[j:]</code>

Better approach using del :

<code>del my_list[i:]
del my_list[:j]</code>

Zip operation with the longest iterable

<code>list(zip('abc', [1, 2, 3, 4]))</code>

Result contains elements up to the shortest iterable. To use the longest iterable, employ itertools.zip_longest :

<code>from itertools import zip_longest
list(zip_longest('abc', [1, 2, 3, 4]))</code>

Copying lists

Shallow copy via slicing:

<code>thy_list = my_list[:]</code>

Deep copy using copy.deepcopy :

<code>import copy
thy_list = copy.deepcopy(my_list)</code>

Apply a function to multiple iterables with map

<code>my_list = [11, 13, 15, 17]
thy_list = [2, 4, 6, 8, 10]
list(map(lambda x, y: x + y, my_list, thy_list))</code>

Equivalent using list comprehension and zip :

<code>my_list = [11, 13, 15, 17]
thy_list = [2, 4, 6, 8, 10]
[x + y for x, y in zip(my_list, thy_list)]</code>

Remove falsy values (None, 0, empty) from a list

<code>list(filter(bool, my_list))</code>

Or using a list comprehension:

<code>[x for x in my_list if x]</code>

Extract a specific column from a nested list (matrix)

<code>my_list = [
    [1, 1, 2, 2],
    [5, 6, 7, 8],
    [3, 3, 4, 4],
]
col1, *_ = zip(*my_list)
list(col1)  # => [1, 5, 3]</code>

Similarly, to get the second column:

<code>_, col2, *_ = zip(*my_list)
list(col2)  # => [1, 6, 3]</code>

Transpose a matrix

<code>[list(x) for x in zip(*my_list)]</code>

The above yields the transposed matrix as a list of rows.