Agfdhyk

From two dictionaries:

d1 = {a:a for a in 'abcdefg'}

d2 = {n:n for n in range(10)}

How can I create a third one like:

new_dict = {k:d1[k] if k in d1.keys() else k:d2[k]  for k in 'abc123' }

It's throwing a syntax Error, but with list comprehension seems to be fine:

[a if a else 2 for a in [0,1,0,3]]

out: [2, 1, 2, 3]

Moreover, why this works:

{k:d1[k]  for k in 'abc123' if k in d1.keys() }

and this doesn't:

{k:d1[k] if k in d1.keys() for k in 'abc123' }

You can't use the key-value pair in the else part of ternary conditional like so.

Do this instead:

new_dict = {k: d1[k] if k in d1 else d2[int(k)]  for k in 'abc123'}

#                                    ^^<- make value d2[int(k)] on else

print(new_dict)

#{'2': 2, '1': 1, 'b': 'b', 'a': 'a', 'c': 'c', '3': 3}

Note that if k in d1 checks if k is a key in the dictionary d1. No need to call the keys method.

As described, it seems like both your d1 and d2 are artifacts of how you envision solving the problem and aren't essential. How about simply:

>>> dictionary = {k: int(k) if k.isdigit() else k for k in 'abc123'}

>>> dictionary

{'b': 'b', '3': 3, '2': 2, '1': 1, 'a': 'a', 'c': 'c'}

>>> 

Or is there more to the problem you're trying to solve?

This is a general answer for dictionary comprehension with "else". I came across this post when I google-searched it, so I hope it helps future googlers.

So lets say I want to create dictionary with a condition on both k and v

A naive way to solve this would look something like this:

{k:v if (condition) else otherk:otherv for k,v in some_dictionary}

This doesn't work, as mentioned before by Moses Koledoye.

However, you can use the following for each part:

{k if condition1 else otherK: v if condition2 else otherV for k,v in some_dictionary}

Note that here, we conditional the key's assignment and the value's assignment.
The most important thing to pay attention to here is the location of the : delimeter between the keys and the values. Hope this helps.

The following is an example for getting a custom dictionary in the following from:
for the english alphabet
from letters A-G would show a positive value for the order of the upper-case letters
from letters J-Z shows a negative value for the order of the small-case letters

This is an example for different keys and values based on a certain condition.
I hope this is explained well enough.

>>> def less_than_H_ascii_val(x):

...     return x < ord('H')-ord('A')

...

>>> {chr(k+ord('A')) if less_than_H_ascii_val(k) else chr(k+ord('a')):

... k if less_than_H_ascii_val(k) else -k 

... for k in range(26)}

{'A': 0, 'C': 2, 'B': 1, 'E': 4, 'D': 3, 'G': 6, 'F': 5, 'i': -8, 'h': -7, 'k': -10, 'j': -9, 'm': -12, 'l': -11, 'o': -14, 'n': -13, 'q': -16, 'p': -15, 's': -18, 'r': -17, 'u': -20, 't': -19, 'w': -22, 'v': -21, 'y': -24, 'x': -23, 'z': -25}

{k:v1 if condition1 else v2 for k in some_list} 

Which is equal to:

{k:(v1 if condition1 else v2) for k in some_list}

The latter is more easily understood