Simple syntax error in Python if else dict comprehension

Question

I have a set and dictionary and a value = 5

v = s = {\'a\', \'b\', \'c\'}
d = {\'b\':5 //<--new value}

If the key \'b\' in dictionary d

Answer 1

In [82]: s = {'a', 'b', 'c'}

In [83]: d = {'b':5 }

In [85]: {key: d.get(key, 0) for key in s}
Out[85]: {'a': 0, 'b': 5, 'c': 0}

Answer 2

You can't use a ternary if expression for a name:value pair, because a name:value pair isn't a value.

You can use an if expression for the value or key separately, which seems to be exactly what you want here:

{k: (d[k] if k in v else 0) for k in v}

However, this is kind of silly. You're doing for k in v, so every k is in v by definition. Maybe you wanted this:

{k: (d[k] if k in v else 0) for k in d}

Answer 3

The expanded form of what you're trying to achieve is

a = {}
for k in v:
    a[k] = d[k] if k in d else 0

where d[k] if k in d else 0 is the Python's version of ternary operator. See? You need to drop k: from the right part of the expression:

{k: d[k] if k in d else 0 for k in v} # ≡ {k: (d[k] if k in d else 0) for k in v}

You can write it concisely like

a = {k: d.get(k, 0) for k in d}

Answer 4

This should solve your problem:

>>> dict((k, d.get(k, 0)) for k in s)
{'a': 0, 'c': 0, 'b': 5}