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 max(my_dict.values()) Get the key of the maximum value: max(my_dict, key=my_dict.get) Get both the key and value of the maximum entry: max(my_dict.items(), key=lambda x: x[1]) Alternative using operator.itemgetter:

import operator
max(my_dict.items(), key=operator.itemgetter(1))

Count occurrences of each element in a list {x: my_list.count(x) for x in set(my_list)} Or using itertools.groupby:

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

Or using collections.Counter:

from collections import Counter
dict(Counter(my_list))

Truncate a list efficiently

my_list = my_list[:i]
my_list = my_list[j:]

Better approach using del:

del my_list[i:]
del my_list[:j]

Zip operation with the longest iterable list(zip('abc', [1, 2, 3, 4])) Result contains elements up to the shortest iterable. To use the longest iterable, employ itertools.zip_longest:

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

Copying lists

Shallow copy via slicing: thy_list = my_list[:] Deep copy using copy.deepcopy:

import copy
thy_list = copy.deepcopy(my_list)

Apply a function to multiple iterables with map

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

Equivalent using list comprehension and zip:

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

Remove falsy values (None, 0, empty) from a list list(filter(bool, my_list)) Or using a list comprehension: [x for x in my_list if x] Extract a specific column from a nested list (matrix)

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

Similarly, to get the second column:

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

Transpose a matrix [list(x) for x in zip(*my_list)] The above yields the transposed matrix as a list of rows.