检查是一个元组，值在python列表中

Question

Say I have a list of tuples in python (name, age).

I want to check if there is a tuple in that list with "Mary" as the name, I don't care what the age is.

How do I do this efficiently?

Answer 1

any(a == 'Mary' for a, b in tuples) # check if any tuple has a name equal to Mary

Answer 2

If you are going to be doing many lookups make a set of the names:

st = {name for name,_ in lst}

Then just check if name in st :...

Set lookups are 0(1) using any for loop is going to be linear, if you always keep a set of names updating if a new tuple gets added then it will be a lot more efficient.

If you actually plan on using the tuple with the name in it then you will have to iterate over the list of tuples and check each name.

Answer 3

If you must have a list then you're going to be stuck with O(n) (assuming the list is unsorted):

my_tuple = ("Mary", 30)
my_list = [("Amber", 15), ("Mary", 25)]

def find_tuple(tuple_, list_):
    for val in list_:
        if val[0] == tuple_[0]:
            return val
    return None

Otherwise, if your data-structure is flexible, use a dictionary:

my_tuple = ("Mary", 30)
my_dict = {"Amber": ("Amber", 15), "Mary": ("Mary", 25)}

def find_tuple(tuple_, dict_):
    return dict_.get(tuple_[0], None)

Answer 4

Another possibility is to make a list of just the names and use the in operator:

names = [name for name, _ in tuples]
answer = "mary" in names