env: python\r: No such file or directory

Question 1

The script contains CR characters. The shell interprets these CR characters as arguments.

Solution: Remove the CR characters from the script using the following script.

with open('beak', 'rb+') as f:
    content = f.read()
    f.seek(0)
    f.write(content.replace(b'\r', b''))
    f.truncate()

Question 2

Open the file in vim or vi, and administer the following command:

:set ff=unix

Save and exit:

:wq

Done!

Explanation

ff stands for file format, and can accept the values of unix (\n), dos (\r\n) and mac (\r) (only meant to be used on pre-intel macs, on modern macs use unix).

To read more about the ff command:

:help ff

:wq stands for Write and Quit, a faster equivalent is Shift+zz (i.e. hold down Shift then press z twice).

Both commands must be used in command mode.

Usage on multiple files

It is not necessary to actually open the file in vim. The modification can be made directly from the command line:

 vi +':wq ++ff=unix' file_with_dos_linebreaks.py

To process multiple *.py files (in bash):

for file in *.py ; do
    vi +':w ++ff=unix' +':q' "${file}"
done

^{😱 offtopic: if by chance you are stuck in vim and need to exit, here are some easy ways.}

Removing the BOM mark

Sometimes even after setting unix line endings you might still get an error running the file, especially if the file is executable and has a shebang. The script might have a BOM marker (such as 0xEFBBBF or other) which makes the shebang invalid and causes the shell to complain. In these cases python myscript.py will work fine (since python can handle the BOM) but ./myscript.py will fail even with the execution bit set because your shell (sh, bash, zsh, etc) can't handle the BOM mark. (It's usually windows editors such as Notepad which create files with a BOM mark.)

The BOM can be removed by opening the file in vim and administering the following command:

:set nobomb

Question 3

You can convert the line ending into *nix-friendly ones with

dos2unix beak

Question 4

If you use PyCharm you can easily solve it by set the line separator to LF. See my screenshot.

Question 5

The answer of falsetru did absolutely solve my problem. I wrote a small helper that allows me to normalize line-endings of multiple files. As I am not very familar with the line-endings stuff on multiple platforms, etc. the terminology used in the program might not be 100% correct.

#!/usr/bin/env python
# Copyright (c) 2013  Niklas Rosenstein
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

import os
import sys
import glob
import argparse

def process_file(name, lend):
    with open(name, 'rb') as fl:
        data = fl.read()

    data = data.replace('\r\n', '\n').replace('\r', '\n')
    data = data.replace('\n', lend)
    with open(name, 'wb') as fl:
        fl.write(data)

def main():
    parser = argparse.ArgumentParser(description='Convert line-endings of one '
            'or more files.')
    parser.add_argument('-r', '--recursive', action='store_true',
            help='Process all files in a given directory recursively.')
    parser.add_argument('-d', '--dest', default='unix',
            choices=('unix', 'windows'), help='The destination line-ending '
            'type. Default is unix.')
    parser.add_argument('-e', '--is-expr', action='store_true',
            help='Arguments passed for the FILE parameter are treated as '
            'glob expressions.')
    parser.add_argument('-x', '--dont-issue', help='Do not issue missing files.',
            action='store_true')
    parser.add_argument('files', metavar='FILE', nargs='*',
            help='The files or directories to process.')
    args = parser.parse_args()

    # Determine the new line-ending.
    if args.dest == 'unix':
        lend = '\n'
    else:
        lend = '\r\n'

    # Process the files/direcories.
    if not args.is_expr:
        for name in args.files:
            if os.path.isfile(name):
                process_file(name, lend)
            elif os.path.isdir(name) and args.recursive:
                for dirpath, dirnames, files in os.walk(name):
                    for fn in files:
                        fn = os.path.join(dirpath, fn)
                        process_file(fn, fn)
            elif not args.dont_issue:
                parser.error("File '%s' does not exist." % name)
    else:
        if not args.recursive:
            for name in args.files:
                for fn in glob.iglob(name):
                    process_file(fn, lend)
        else:
            for name in args.files:
                for dirpath, dirnames, files in os.walk('.'):
                    for fn in glob.iglob(os.path.join(dirpath, name)):
                        process_file(fn, lend)

if __name__ == "__main__":
    main()

Question 6

I cured this error by running python3, ie python3 \path\filename.py