Why does dict(k=4, z=2).update(dict(l=1)) return None in Python?

dictionary, python, python-2.7

Solution

The `.update()` method alters the dictionary in place and returns `None`. The dictionary itself is altered, no altered dictionary needs to be returned.

Assign the dictionary first:

a_dict = dict(k=4, z=2)
a_dict.update(dict(l=1))
print a_dict

This is clearly documented, see the `dict.update()` method documentation:

Update the dictionary with the key/value pairs from other, overwriting existing keys. Return `None`.

Problem

Original source

Related problems

• Why doesn't a python dict.update() return the object?
• Why doesn't a python dict.update() return the object?