Convert every character in a String to a Dictionary Key

Question

Suppose i have a string "abcdefghijklmnopqrstuvwxyz"and i want to initialize dictionary keys with those values.

alphabet = 'abcdefghijklmnopqrstuvwxyz'

alphabetDict = dict()
for char in alphabet:
    alphabetDict[char] = 0

Is there a better way of doing that?

Answer 1

You can use dict.fromkeys() method -

>>> s = 'abcdefghijklmnopqrstuvwxyz'
>>> alphaDict = dict.fromkeys(s,0)
>>> alphaDict
{'m': 0, 'p': 0, 'i': 0, 'n': 0, 'd': 0, 'w': 0, 'k': 0, 'y': 0, 's': 0, 'b': 0, 'h': 0, 't': 0, 'u': 0, 'q': 0, 'g': 0, 'l': 0, 'e': 0, 'a': 0, 'j': 0, 'c': 0, 'o': 0, 'f': 0, 'v': 0, 'x': 0, 'z': 0, 'r': 0}

From documentation -

fromkeys(seq[, value])

Create a new dictionary with keys from seq and values set to value.

fromkeys() is a class method that returns a new dictionary. value defaults to None.

Please note, you should not use this if value is something mutable like list or another dict , etc. As the value is only evaluted once when you call the method fromkeys() , and all keys point to the same object.

You can use this for immutable types as value like int, str , etc.

---

Also, you do not need to specify the s or alphabet string, you can instead use string.ascii_lowercase . Example -

>>> import string
>>> alphaDict = dict.fromkeys(string.ascii_lowercase,0)
>>> alphaDict
{'m': 0, 'p': 0, 'i': 0, 'n': 0, 'd': 0, 'w': 0, 'k': 0, 'y': 0, 's': 0, 'b': 0, 'h': 0, 't': 0, 'u': 0, 'q': 0, 'g': 0, 'l': 0, 'e': 0, 'a': 0, 'j': 0, 'c': 0, 'o': 0, 'f': 0, 'v': 0, 'x': 0, 'z': 0, 'r': 0}

Answer 2

You can use dictionary comprehensions in Python.

alphabetDict = {char: 0 for char in alphabet}

Dictionaries (Python Docs)

There is a minor difference between this answer and Anand's above. Dict comprehensions evaluate the value for every key, while fromkeys only does it once. If you're using things like ints, this poses no problem. However, if you do

d = {key: [] for key in <some set>}
d[3].append(5)
print(d[2])

gives you

[]

and you have distinct lists, while

d = dict.fromkeys(<some set>, [])
d[3].append(5)
print(d[2])

gives you

[5]

will map all the keys to the same list.

Answer 3

Yes, you can do that in one line using dictionary comprehensions.

In [1]: alphabet = 'abcdefghijklmnopqrstuvwxyz'

In [2]: {x:0 for x in alphabet} # dictionary comprehension
Out[2]: 
{'a': 0,
 'b': 0,
 'c': 0,
 'd': 0,
 'e': 0,
 'f': 0,
 'g': 0,
 'h': 0,
 'i': 0,
 'j': 0,
 'k': 0,
 'l': 0,
 'm': 0,
 'n': 0,
 'o': 0,
 'p': 0,
 'q': 0,
 'r': 0,
 's': 0,
 't': 0,
 'u': 0,
 'v': 0,
 'w': 0,
 'x': 0,
 'y': 0,
 'z': 0}