Command-line counter in Python

Part of the big counter example project, let's see the simple command line counter for a single number implemented in Python.

examples/python/counter.py

import os

counter_file = 'counter.txt'
if os.path.exists(counter_file):
    with open(counter_file) as fh:
        count = int(fh.read())
else:
    count = 0

count += 1
print(count)

with open(counter_file, 'w') as fh:
    fh.write(str(count))

The os.path.exists method checks if a file exists.

Normally in Python if we open a file it does not get closed automatically. If we forget to call close all kinds of bad things can happen.

In order to force the call of close it is recommended to wrap any file operation in a with statement. The with statement arranges the close method to be called on the filehandle when the execution leaves the code inside the with statement.

open defaults to read-only.

The read method reads in the whole content of the file which in our case is just a number.

By default everything we read from a file is considered as a string. We can use the int function to convert the value to Integer.

In Python there is no ++ so we use the += 1 construct to increment the number by one.

In order to save the new counter in the file, first we need to open the file for writing using open(filename, 'w') and then we can use the write method to actually write out the data. It expects a string so we need to convert our Integer to String using the str function.

No need to explicitly close the file as leaving the with statement will automatically call the close method.