Merge two hashes/dictionaries in Ruby and Python.

merge.rb

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h3 = h1.merge(h2)   
h3 #=> {"a"=>100, "b"=>254, "c"=>300}
h1 #=> { "a" => 100, "b" => 200 }

update.py

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

That's only valid syntax in Python 3.5. In Python 2, you could do

x = {'a': 1}
y = {'b': 2}
z = dict(x, **y)

x = {**x, **y} # not the same as
x.update(y)  
# because a new dict is constructed and assigned to x

x = {'x': 'xxxx'}

y = {'y': 'yyyy'}

id(x), id(y)

(140215338406176, 140215338368816)

x = {**x, **y}; x

{'x': 'xxxx', 'y': 'yyyy'}

id(x)

140215338405960