Check For The Existence Of A String In A List Of Tuples By Specific Index

If I have: my_list = [('foo', 'bar'), ('floo', 'blar')] how can I easily test if some string is in the first element in any of those tuples? something like: if 'foo' in my_list w

Solution 1:

If you want to check only against the first item in each tuple:

if'foo' in (item[0] foritemin my_list)

Alternatively:

ifany('foo' == item[0] for item in my_list)

Solution 2:

You can first extract a list of only the first items and then perform a check:

>>>my_list = [('foo', 'bar'), ('floo', 'blar')]>>>'foo'inlist(zip(*my_list))[0]
True

Alternatively:

>>> 'foo'innext(zip(*my_list))
True

Solution 3:

Use the batteries:

importoperatorif'foo'in map(operator.itemgetter(0), my_list):

This won't create a copy of your list and should be the fastest.

Solution 4:

if'foo' in map(lambda x: x[0], my_list):
    <do something>

map takes each element in the list, applies a function to it, and returns a list of the results. In this case, the function is a lambda function that just returns the first sub element of the original element.

((0,1),(3,4)) becomes (0,3).

Solution 5:

my_list = iter(my_list)

result = FalsewhileTrue:
    try:
        x, y = my_list.next()
        if x == 'foo':
            result = Truebreakexcept StopIteration:
        break