please help me with this code in pythone

[chakerer]

Body

so im doing this tesk here in the image,
and when i created the code ,`from collections import defaultdict

num = input().split()
n = int(num[0])
m = int(num[1])
c_n = 0
c_m = 0
a = []
b = []
while c_n < n:
 A = str(input()).lower() 
 a.append(A)
 c_n +=1

while c_m < m:
 B = str(input()).lower()
 b.append(B)
 c_m +=1

d = defaultdict(list)

def compare ():
    
    for i in b:
        if i in a:
            for index,j in enumerate(a,1) :
             if j == i :
              d[i].append(index)
            print(" ".join (map (str,d[i])))
        else: 
            print("-1")     
    
            
compare ()`

that code worked in 7/10 cases only, but when i chagen this part `

for index,j in enumerate(a,1) :
             if j == i :
              d[i].append(index)

with is list comprehension d[i] = [index for index,j in enumerate(a,1) if j == i]
the code works on 10/10 of the cases please can any one expalin why please ? whats the deffrance, and thank you

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[chakerer]

Thanks for your reply, yes i know that, but i want to know why or how the list comprehension is working in all cases but the normal fo loop is not, although they are the exacte same expresion technically they should do the same thing but in reality it is not , the list comprehension is ding better why or how please ?

[ljstein99]

The difference you're observing may stem from how each method handles memory and variable scope. The list comprehension is evaluated freshly each time it's run, ensuring that d[i] is assigned a newly created list that directly reflects the current state of a. This avoids any potential side effects from previous iterations or external modifications to the list that d[i] might reference.

On the other hand, the loop version uses append(), which modifies the list in place. If there's any unintended interaction with d[i] elsewhere in your code or if the initialization of d isn't handled properly, it could lead to discrepancies in how data is accumulated during each iteration. Therefore, the list comprehension not only ensures a clean slate with each assignment but is also often more efficient in execution, which might explain why it performs correctly in all test cases.

[chakerer]

The difference you're observing may stem from how each method handles memory and variable scope. The list comprehension is evaluated freshly each time it's run, ensuring that d[i] is assigned a newly created list that directly reflects the current state of a. This avoids any potential side effects from previous iterations or external modifications to the list that d[i] might reference.

On the other hand, the loop version uses append(), which modifies the list in place. If there's any unintended interaction with d[i] elsewhere in your code or if the initialization of d isn't handled properly, it could lead to discrepancies in how data is accumulated during each iteration. Therefore, the list comprehension not only ensures a clean slate with each assignment but is also often more efficient in execution, which might explain why it performs correctly in all test cases.

thank you so much for the reply, yes i think you right, i just find out that the reason is the tesk it slfe had a condition that the code should do the tesk in a limited time , so when i use list comprehension it is more efficient as you said so it is much faster then a for loop and this si why it works in all cases unlike for loop, thank you,