self modifying python script

Question

I want to create python script which can modify code in that script itself using Python Language Services or using any other way.
e.g. A script which keep track of its count of successfull execution

import re
COUNT = 0

def updateCount():
    # code to update second line e.g. COUNT = 0
    pass

if __name__ == '__main__':
    print('This script has run {} times'.format(COUNT))
    updateCount()

On successful execution of this script code should get changed to

import re
COUNT = 1

def updateCount():
    # code to update second line e.g. COUNT = 0
    pass

if __name__ == '__main__':
    print('This script has run {} times'.format(COUNT))
    updateCount()

Simple approach came to my mind was to open __file__ in write mode and do requried modification using reguler expessions etc. But that did not work I got exception io.UnsupportedOperation: not readable. Even if this approach would be working then it would be very risky because it can spoil my whole script. so I am looking for solution using Python Language Services.

Answer 1

Yes, you can use the language services to achieve self-modification, as in following example:

>>> def foo(): print("original foo")
>>> foo()
original foo
>>> rewrite_txt="def foo(): print('I am new foo')"
>>> newcode=compile(rewrite_text,"",'exec')
>>> eval(newcode)
>>> foo()
I am new foo

So, by new dynamically generated code you can replace stuff contained in the original source file, without modifying the file itself.

Answer 2

A python script is nothing more than a text file. So, you are able to open it as an external file and read & write on that. (Using __file__ variable you can get the exact name of your script):

def updateCount():
    fin = open(__file__, 'r')
    code = fin.read()
    fin.close()

    second_line = code.split('\n')[1]
    second_line_parts = second_line.split(' ')
    second_line_parts[2] = str(int(second_line_parts[2])+1)

    second_line = ' '.join(second_line_parts)
    lines = code.split('\n')
    lines[1] = second_line
    code = '\n'.join(lines)

    fout = open(__file__, 'w')
    fout.write(code)
    fout.close()