Python Dictionary Comprehensions Made Simple

So, you are getting good at Python dictionaries, but you must keep stepping up the ladder.

Copying each key and value to another dictionary

Traditional way:

a = {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}
b = {}
for k, v in a.items():
    b[k] = v
print(b)
>>> {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}

Using Dictionary Comprehensions:

a = {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}
b = {k: v for k, v in a.items()}
print(b)
>>> {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}

Copying each key and value to another dictionary if a certain condition is met

Traditional way:

a = {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}
b = {}
for k, v in a.items():
    if v > 1:
        b[k] = v
print(b)
>>> {'ho': 2, "let's": 3, 'go': 4}

Using Dictionary Comprehensions:

a = {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}b = {k: v for k, v in a.items() if v > 1}
print(b)
>>> {'ho': 2, "let's": 3, 'go': 4}

Converting two lists to one Dictionary

Traditional way:

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = {}
for item in a:
    c[item] = b[a.index(item)]
print(c)
>>> {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}

Using Dictionary Comprehensions:

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = {k: v for k, v in zip(a, b)}
print(c)
>>> {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}

Using dict and zip (even simpler):

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = dict(zip(a, b))
print(c)
>>> {'hey': 1, 'ho': 2, "let's": 3, 'go': 4}

Finally, converting 3 lists to 1 dictionary with the last 2 lists as 1 value

Traditional way:

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = ['a', 'b', 'c', 'd']
d = {}
for item in a:
    d[item] = [b[a.index(item)], c[a.index(item)]]
print(d)
>>> {'hey': [1, 'a'], 'ho': [2, 'b'], "let's": [3, 'c'], 'go': [4, 'd']}

Using Dictionary Comprehension with zip:

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = ['a', 'b', 'c', 'd']
e = { k: list(v) for k, v in zip(a, zip(b, c)) }
print(e)
>>> {'hey': [1, 'a'], 'ho': [2, 'b'], "let's": [3, 'c'], 'go': [4, 'd']}

Using dict, zip and map (much simpler):

a = ['hey', 'ho', "let's", "go"]
b = [1, 2, 3, 4]
c = ['a', 'b', 'c', 'd']
d = dict(zip(a, map(list, zip(b, c))))
print(d)
>>> {'hey': [1, 'a'], 'ho': [2, 'b'], "let's": [3, 'c'], 'go': [4, 'd']}

Conclusion

I hope you learned something new today, by learning this article.

Have you ever used any of these? Please let me know in the comments. You can also follow me here, so you can track what’s next to come.

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