如何比较python中的两个列表并通过电子邮件返回匹配项

Question

I want to compare email into both list and put into new list,

a = [('abc@gmail.com',5),('xyz@gmail.com',6),('pqr@gmail.com',8)]

b = [('ABC','abc@gmail.com'),('XYZ','xyz@gmail.com'),('PQR','pqr@gmail.com')]

would return [('ABC',5),('XYZ',6),('PQR',8)] , for instance.

Answer 1

Lookup in a list for each item if not already ordered is O(n) complexity and is not an ideal data structure for the process

It would be beneficial if you would convert the list you would be using for lookup converted to a dictionary

d_a = dict(a)

subsequent to which the lookup is both efficient and elegant

>>> [(key, d_a[value]) for key, value in b if value in d_a]
[('ABC', 5), ('XYZ', 6), ('PQR', 8)]

You should also take into consideration for negative case when the lookup key may not match or is present in the lookup list

Answer 2

Sorting both lists and using list comprehension:

a = [('abc@gmail.com',5),('xyz@gmail.com',6),('pqr@gmail.com',8)]

b = [('ABC','abc@gmail.com'),('XYZ','xyz@gmail.com'),('PQR','pqr@gmail.com')]

result = [(y[0],x[1]) for x,y in zip(sorted(a,key=lambda s:s[0])), sorted(b,key=lambda s:s[1])) if x[0]==y[1]]

list a is sorted based on first element( s[0] ) of each tuple.

list b is sorted based on second element( s[1] ) of each tuple.