CODEWITHSUNDEEP
pythonpython-3.xfile-handlingwith-statement
ashish_k
ashish_k

Reputation: 1581

Unable to loop over a file using context manager python3

instances = ['XYZ']
curr_date = time.strftime("%Y%m%d")
    
    for inst_name in instances:
        with open(f'results_{inst_name}_master.csv') as f:
            pkt_name = f.readline().split(';')[1]
            print(f"package name is: {pkt_name}")
            run_dt = f.readline().split(';')[1]
            print(f"run date: {run_dt}")
            time_check = f.readlines()[1].split(';')[-5].split(':')[0]
            print(f"time is : {time_check}")
            if ((run_dt == curr_date) or (run_dt < curr_date and time_check in range(20,24))):
                for index, l in enumerate(f, 1):
                    if 'remoteInstallation' in l:
                        print(l)

Sample file:

pktName;sample-quality.zip;
RunDate;20220116;
sample:path_to_test\test;20220116;01:29:13;20220114;01:33:36;0:04:22;
;sample:path\to\remoteInstallation;45.99;../logs_path/index.html;OK;
;sample:path\to\remoteInstallation;42.87;../logs__other_path/index.html;1

I'm getting all the results except print(l), that is , it's unable to loop over the file although the string : 'remoteInstallation' is present in the file.

Please note that in actual, the file contains the newline characters(\n) at the end of each line.

What am i doing wrong here?

Thanks in advance!

Upvotes: 0

Views: 142

Answers (1)

E. Ducateme
E. Ducateme

Reputation: 4248

It appears that you are using readlines() instead of .readline() on the time_check line.

import time
instances = ['XYZ']
curr_date = time.strftime("%Y%m%d")

for inst_name in instances:
    with open(f'results_{inst_name}_master.csv') as f:
        pkt_name = f.readline().split(';')[1]
        print(f"package name is: {pkt_name}")
        run_dt = f.readline().split(';')[1]

This line appears to be incorrect. It calls readlines and references the element at the first index. I removed the s and the index reference.

        time_check = f.readline().split(';')[-5].split(':')[0]  

        print(f"time is : {time_check}")
        if ((run_dt == curr_date) or (run_dt < curr_date and time_check in range(20,24))):
            for index, l in enumerate(f, 1):
                if 'remoteInstallation' in l:
                    print(l)

What happened behind the scenes?

For file objects (in this case f) there is an internal pointer that keeps track of where in the file the script is currently looking. This pointer is universal and used by multiple functions and by for loops.

Each call to readline() will read a line from the file and move the pointer to the next line. Any call to readlines() will read all the lines until the end of the file and move the pointer to the end of the file. For loops read the next line (if there is one) and keep repeating that process until the pointer is at the end of the file. In our code, this line:

for index, l in enumerate(f, 1):

is a for loop that is attempting to read more lines from the file.

Unfortunately, in our case, by calling readlines(), we have already read all the lines from file and have already moved the pointer to the end of the file and thus the for loop was unable to read in any new lines.

Upvotes: 1

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