Answer to Question #101041 in Python for Bella

Question

Describe how catching exceptions can help with file errors. Write three Python examples that
actually generate file errors on your computer and catch the errors with try: except: blocks.
Include the code and output for each example in your post.
Describe how you might deal with each error if you were writing a large production program. These
descriptions should be general ideas in English, not actual Python code.

Answer 1

"""
Catching exceptions helps a programmer to resolve raised issues at runtime
instead of deliberately сlosing their program.

There are a lot of types of file errors. e.g. hadware/os errors, name errors,
operation errors, data errors. Many of them can be processed in Python as in any
other language.
"""
import os
import errno
import io
import sys
# dirname and filename and path
dn, fn = 'foo', 'bar.txt'
pn = os.path.join(dn, fn)

def pre():
    # https://docs.python.org/3/library/os.html#os.makedirs
    os.makedirs(dn, exist_ok=True)
    # https://docs.python.org/3/library/functions.html?open#open
    # https://docs.python.org/3/library/io.html#io.IOBase.close
    open(pn, 'w').close()

def example1():
    # https://docs.python.org/3/library/os.html#os.mkdir
    try:
        os.mkdir(dn)
    # https://docs.python.org/3/library/exceptions.html#OSError
    except OSError as e:
        # https://docs.python.org/3/library/errno.html
        if e.errno != errno.EEXIST:
            raise
        else:
            print('The directory already exitst')

def example2():
    with open(pn, 'r') as inp:
        try:
            # https://docs.python.org/3/library/io.html#io.TextIOBase.write
            inp.write('test')
        # https://docs.python.org/3/library/io.html#io.UnsupportedOperation
        except io.UnsupportedOperation:
            print('Can\'t change a readonly file')

def example3():
    # not a real example
    with open(pn, 'r') as inp:
        # https://docs.python.org/3/library/sys.html?#sys.stdin
        old = sys.stdin
        sys.stdin = inp
        try:
            # https://docs.python.org/3/library/functions.html#input
            text = input()
        # https://docs.python.org/3/library/exceptions.html#EOFError
        except EOFError:
            print('Unable to read anything')
        finally:
            sys.stdin = old

def post():
    # pn = 'aaa'
    try:
        # https://docs.python.org/3/library/os.html#os.remove
        os.remove(pn)
    except:
        # https://docs.python.org/3/library/sys.html#sys.exc_info
        print(sys.exc_info()[1])
    try:
        # https://docs.python.org/3/library/os.html#os.rmdir
        os.rmdir(dn)
    except:
        print(sys.exc_info()[1])

def main():
    try:
        pre()
        example1()
        example2()
        example3()
    finally:
        post()

if __name__ == '__main__':
    main()