How do I merge two dictionaries in a single expression in Python

Question

I have two Python dictionaries, and I want to write a single expression that returns these two dictionaries, merged. The update() method would be what I need, if it returned its result instead of modifying a dictionary in-place.

>>> x = {'a': 1, 'b': 2}
>>> y = {'b': 10, 'c': 11}
>>> z = x.update(y)
>>> print(z)
None
>>> x
{'a': 1, 'b': 10, 'c': 11}

How can I get that final merged dictionary in z, not x?

Answer 1

Hello,

For dictionaries x and y, z becomes a shallowly merged dictionary with values from y replacing those from x.

• In Python 3.5 or greater:

  z = {**x, **y}

• In Python 2, (or 3.4 or lower) write a function:

  def merge_two_dicts(x, y):
      z = x.copy()   # start with x's keys and values
      z.update(y)    # modifies z with y's keys and values & returns None
      return z

  and now:

  z = merge_two_dicts(x, y)

Hope this works!!

Thank you!!