Check list of tuples where first element of tuple is specified by defined string

Question

This question is similar to Check that list of tuples has tuple with 1st element as defined string but no one has properly answered the "wildcard" question.

Say I have [('A', 2), ('A', 1), ('B', 0.2)]

And I want to identify the tuples where the FIRST element is A. How do I return just the following?

[('A', 2), ('A', 1)]

Answer 1

Using a list comprehension:

>>> l = [('A', 2), ('A', 1), ('B', 0.2)]
>>> print([el for el in l if el[0] == 'A'])
[('A', 2), ('A', 1)]

Answer 2

Simple enough list comprehension:

>>> L = [('A', 2), ('A', 1), ('B', 0.2)]
>>> [(x,y) for (x,y) in L if x == 'A']
[('A', 2), ('A', 1)]

Answer 3

You could use Python's filter function for this as follows:

l = [('A', 2), ('A', 1), ('B', 0.2)]
print filter(lambda x: x[0] == 'A', l)

Giving:

[('A', 2), ('A', 1)]