Problem in reading file using `with` operator in python

Question

I have a code which is using with statement to read a file line by line. The below code goes in infinite loop where line:1 is printed everytime. Not sure what mistake I am doing

  with open (config_file) as fp:
        line = fp.readline()
        print("line is", line)
        while line:
            match = re.search("^QueueDir\s*=\s*(.*)$", line)
            if (match.group(1)):
                return match.group(1)

you must give mode of operation while executing ```with``` statement — Akshat Zala, Jul 23 '20 at 10:53
@Akshat No, the default mode of [`open`](https://docs.python.org/3/library/functions.html#open) is `'r'`, which is fine here. — tripleee, Jul 23 '20 at 11:47

score 1 · Answer 1 · edited Jul 23 '20 at 12:21

1

Your variable fp is a file handle, use for loop for easy access of elements in the loop.

with open (config_file) as fp:
    for line in fp:
        match = re.search("^QueueDir\s*=\s*(.*)$", line)
        if (match.group(1)):
            return match.group(1)

The code goes to infinite loop because of the while condition, while line:, in the case of conditions, any non-zero values are considered as True, so as line is non-empty, the condition is interpreted as while True, so it runs infinitely.

edited Jul 23 '20 at 12:21

tripleee

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answered Jul 23 '20 at 10:51

Roshin Raphel

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1

`lines = fp.readline()` only reads one line. Your `for` loop ends up iterating over its individual characters. You want `for line in fp:` instead, plain and simple. Also, the `print` refers to an uninitialized variable. – tripleee Jul 23 '20 at 11:52
@tripleee `print("line is", line)` came from OP's code, I didn't notice it, my mistake. – Roshin Raphel Jul 23 '20 at 11:57
1

"Your variable is a list" is still not true, but I guess you can fix that too. – tripleee Jul 23 '20 at 12:08

score 0 · Answer 2 · edited Jul 23 '20 at 14:22

add line = fp.readline() at the end of your while loop. As line does not changes from one loop to the next.

  with open (config_file) as fp:
        line = fp.readline()
        print("line is", line)
        while line:
            match = re.search("^QueueDir\s*=\s*(.*)$", line)
            if (match.group(1)):
                return match.group(1)
            line = fp.readline()

Problem in reading file using `with` operator in python

2 Answers2