A little confuse

[infotechsys]

When I run this code in the pdb it works.
accountNbr = 1
for testLine in ftest.readlines():
acct = testLine[1:2] #there account number
if accountNbr == int(acct):
accountNbr = accountNbr + 1

When I run without the debugger I get this error.

File "./casco.py", line 62, in process
if accountNbr == int(acct):
ValueError: invalid literal for int(): "

Can someone explain?