Python 从元组集中检索列表中的值

Question

Suppose I have a ordered list here called T

T = ['foo', 'bar', 'cad']

I then have a set M containing tuples.

M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

For every item in T, I want to find the corresponding tuple pair in M. So my output would look like the following list

O = [ 'bob', 'jack', 'let' ]

I tried this set comprehension but this of course just iterated the elements as defined in the order of M, I need to define it in the order of T.

answer = [ a for (a,b) in R if b in T ]

As a follow up question, say my M looked like:

M = { 
        ('bar', 'jack'), 
        ('foo', 'bob'), 
        ('cad', 'let') 
    }

Does this make this easier to solve?

Is it possible to solve this without using a dict? Purely lists, sets and tuples?

Answer 1

T = ['foo', 'bar', 'cad']

M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

d = {k:v for (v,k) in M}

answer = [d[elt] for elt in T]

print(answer)
# ['bob', 'jack', 'let']

Answer 2

T = ['foo', 'bar', 'cad']
M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

# Solution 1 - Order is different everytime
a = [x for (x, y) in M if y in T]
print(a)

# Solution 2 - Give you answer in same order always
MT = {y:x for (x, y) in M}
a = [MT[i] for i in T]
print(a)

You can try this.