Using for loop iteration with If statement

Question

I have a list of multiple items. Need to create a loop that finds an item from the list and prints it out. If item not found prints out only once that it hasn't been found.

 for x in range(len(regs)):
 rex = regs[x]
 if re.match(rex,hostname):
 print (dev[x],'Regex matched')
 break
 else:
 print('wrong format')

Currently it prints out multiple times that it hasn't been found. When it matches the regex it prints out at the end. I only want the If Else to prints "wrong format" once.

currently prints out wrong format wrong format wrong format wrong format wrong format wrong format wrong format "DeviceX Regex matched"

• Andy_101: a simple solution will be to use a flag

Answer 1

Use else with for.

As you are breaking out of the for loop as soon as you find one item, the below code will work fine:

for x in range(len(regs)):
 rex = regs[x]
 if re.match(rex,hostname):
 print (dev[x],'Regex matched')
 break
else:
 # Does not execute only when a break statement
 # is executed inside the for loop.
 print('wrong format')

• Andy_101: just a gentle reminder.. it's not a good practice to use for-else construct but in this case its fine I guess
• Dipen Dadhaniya: Agreed! But in this short and simple code, I think it is fine.

Answer 2

It is printed multiple times, because there are multiple times where the current value does not match. A simple way to fix this is to use a flag, like so:

value_found = False 
for x in range(len(regs)):
 rex = regs[x]
 if re.match(rex,hostname):
 print (dev[x],'Regex matched')
 value_found = True
 break
if not value_found:
 print('wrong_format')

Answer 3

You can maintain a flag variable as follows.

matched = False
for x in range(len(regs)):
 rex = regs[x]
 if re.match(rex, hostname):
 print(dev[x], "Regex matched!")
 matched = True
 break
if not matched:
 print("Wrong format")

Answer 4

I think you can make it shorter using comprehensive list such as:

if len([r for r in regs if re.match(r, hostname)]) == 1:
 print(dev[regs.index([r for r in regs if re.match(r, hostname)][0])], 'Regex matched')
else:
 print('not found')

• Kins: This code does not work if multiple elements match. The first condition should be len(...) >= 1. And you would probably also need to change the statement in the print.

Answer 5

This should solve your problem.

flag = 0 
for x in range(len(regs)):
 rex = regs[x]
 if re.match(rex, hostname):
 print(dev[x], 'Regex matched')
 flag = 1
 break
if flag == 0:
 print('wrong format')