检查元组的列表，其中元组的第一个元素由定义的字符串指定

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. 这个问题类似于检查元组列表是否具有第一个元素作为定义字符串的元组，但没有人正确回答“通配符”问题。

Say I have [('A', 2), ('A', 1), ('B', 0.2)] 说我有[('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? 我想确定FIRST元素为A的元组。如何返回以下内容？

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

Answer 1

Using a list comprehension: 使用列表理解：

>>> 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: 简单的列表理解：

>>> 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: 你可以使用Python的filter函数，如下所示：

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

Giving: 赠送：

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