Suppose that we have a Python dictionary,
x = {'a': 3, 'b': 2, 'c':7}and, we want to add the values i.e. 3 + 2 + 7 = 12.
Here are the three ways to add the values.
Using list comprehension
>>> x = {'a': 3, 'b': 2, 'c':7}
>>> sum([i for i in x.values()])
12Using for loop I
>>> x = {'a': 34, 'b': 2, 'c':7}
>>> total = 0
>>> for i in x.values():
total += iUsing for loop II
>>> x = {'a': 34, 'b': 2, 'c':7}
>>> total = 0
>>> for key in x.keys():
total += x[key]
Why is list comprehension needed?
Surely you can just do:
>>> x = {'a': 3, 'b': 2, 'c':7}
>>> sum(x.values())
12
x.values() creates list itsefl.
Be more pro – use dict builtin iteration:
>>> x = {‘a’: 3, ‘b’: 2, ‘c’:7}
>>> sum(x.itervalues())
12
@kjg: In Python 3, ‘dict’ object has no attribute ‘itervalues’ anymore. values() returns a lightweight set-like object, effectively making it behave like the old iter* methods.