For 循环在 If 语句中 Python

Question

I am using a for-loop within another for-loop to iterate through and compare two data sets. I want to first use the inner for loop to check for a condition and then, if it fails, to print a value from the outer loop.

For example:

for (i) in list_one:

    for (j) in list_two:
        
        if (condition):

            print(j)

if the condition for 'print(j)' fails for all instances in list_two, I want the current value of list_one to be printed. Something like an 'if: for:' statement seems like it would make sense but I'm not sure if those are possible in Python. Thanks for the help

Answer 1

You can just add a fail flag, like

for (i) in list_one:
    fail = True
    for (j) in list_two:
        if (condition):
            fail = False
            print(j)
    if fail:
        print(i)

Answer 2

If you need to print only the first satisfy condition and then break out of the loop, then you can use for... else

for (i) in list_one:
    for (j) in list_two:
        if (condition):
            print(j)
            break
    else:
        print(i)

If you want to print all the values which satisfy the condition in inner loop, you can use one more variable

for (i) in list_one:
    print_i = True
    for (j) in list_two:
        if (condition):
            print(j)
            print_i = False
    if print_i:
        print(i)