Thread by @gusthema

Quick⚡️ Python🐍 trick:
How do you merge two dictionaries?

[55 sec]🤯

1/6🧵

For Python 3.5 and up you can do:

d1 = {"a":1, "b":2}
d2 = {"c":3, "d":4}
d3 = {**d1, **d2}
d3 == {"a": 1, "b": 2, "c":3, "d":4}

Why?

2/6🧵

The ** operator expands the collection, so, you can think it as this:

d1 = {"a":1, "b":2}
d2 = {"c":3, "d":4}
d3 = {**d1, **d2} -> {"a":1, "b":2, "c":3, "d":4}
d3 == {"a": 1, "b": 2, "c":3, "d":4}

3/6🧵

If the merged dicts have repeated keys, the later will update the earlier values:

d1 = {"a":1, "b":2}
d2 = {"b":3, "d":4}
d3 = {**d1, **d2} -> {"a":1, "b":3, "d":4}
d3 == {"a": 1, "b": 3, "d":4}

4/6🧵

This expansion can also be seen on functions

def foo(a, b, c):
return a + b + c

d1 = {"b":1, "c":2}
foo(0, **d1) -> foo(0, 1, 2) -> 3

💡This is a very common pattern when you want pass all the named parameters to a function from a dictionary.

5/6🧵

In Python 3.9, there's a new way of doing a dict merge (PEP-584) python.org/dev/peps/pep-0…

d1 = {"a":1,"b":2}
d2 = {"c":3,"d":4}
d3 = d1 |d2
d3 == {"a": 1, "b": 2, "c":3, "d":4}

The | is much easier to read but 3.9 is still not the default version so it can be risky to use

6/6🧵