Problems Adding Path and Calling External Program from Python

Problems adding path and calling external program from Python

sys.path is the path to Python libraries, not the system PATH to search for binaries. Try changing os.environ['PATH'] instead.

>>> sys.path.append("/opt/local/bin")
>>> os.system("wget")
sh: wget: command not found
32512
>>> os.environ['PATH'] += os.pathsep + '/opt/local/bin'
>>> os.system("wget")
wget: missing URL

Opening external program in python

I've found a solution for my case, I think there is a problem with Flask upload module, my C++ program was on the same path as my uploaded files from flask, so when I changed the program path and used Windows command prompt to start the program, everything worked like a charm.

How do I execute a program from Python? os.system fails due to spaces in path

subprocess.call will avoid problems with having to deal with quoting conventions of various shells. It accepts a list, rather than a string, so arguments are more easily delimited. i.e.

import subprocess
subprocess.call(['C:\\Temp\\a b c\\Notepad.exe', 'C:\\test.txt'])

How do I execute a program or call a system command?

Use the subprocess module in the standard library:

import subprocess
subprocess.run(["ls", "-l"])

The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc...).

Even the documentation for os.system recommends using subprocess instead:

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.

On Python 3.4 and earlier, use subprocess.call instead of .run:

subprocess.call(["ls", "-l"])

python' is not recognized as an internal or external command

You need to add that folder to your Windows Path:

https://docs.python.org/2/using/windows.html Taken from this question.

Running an outside program (executable) in Python?

Those whitespaces can really be a bother. Try os.chdir('C:/Documents\ and\ Settings/') followed by relative paths for os.system, subprocess methods, or whatever...

If best-effort attempts to bypass the whitespaces-in-path hurdle keep failing, then my next best suggestion is to avoid having blanks in your crucial paths. Couldn't you make a blanks-less directory, copy the crucial .exe file there, and try that? Are those havoc-wrecking space absolutely essential to your well-being...?

How to open external programs in Python

The short answer is that os.system doesn't know where to find firefox.exe.

A possible solution would be to use the full path. And it is recommended to use the subprocess module:

import subprocess

subprocess.call(['C:\Program Files\Mozilla Firefox\\firefox.exe'])

Mind the \\ before the firefox.exe! If you'd use \f, Python would interpret this as a formfeed:

>>> print('C:\Program Files\Mozilla Firefox\firefox.exe')
C:\Program Files\Mozilla Firefox
                                irefox.exe

And of course that path doesn't exist. :-)

So either escape the backslash or use a raw string:

>>> print('C:\Program Files\Mozilla Firefox\\firefox.exe')
C:\Program Files\Mozilla Firefox\firefox.exe
>>> print(r'C:\Program Files\Mozilla Firefox\firefox.exe')
C:\Program Files\Mozilla Firefox\firefox.exe

Note that using os.system or subprocess.call will stop the current application until the program that is started finishes. So you might want to use subprocess.Popen instead. That will launch the external program and then continue the script.

subprocess.Popen(['C:\Program Files\Mozilla Firefox\\firefox.exe', '-new-tab'])

This will open firefox (or create a new tab in a running instance).

---

A more complete example is my open utility I publish via github. This uses regular expressions to match file extensions to programs to open those files with. Then it uses subprocess.Popen to open those files in an appropriate program. For reference I'm adding the complete code for the current version below.

Note that this program was written with UNIX-like operating systems in mind. On ms-windows you could probably get an application for a filetype from the registry.

"""Opens the file(s) given on the command line in the appropriate program.
Some of the programs are X11 programs."""

from os.path import isdir, isfile
from re import search, IGNORECASE
from subprocess import Popen, check_output, CalledProcessError
from sys import argv
import argparse
import logging

__version__ = '1.3.0'

# You should adjust the programs called to suit your preferences.
filetypes = {
    '\.(pdf|epub)$': ['mupdf'],
    '\.html$': ['chrome', '--incognito'],
    '\.xcf$': ['gimp'],
    '\.e?ps$': ['gv'],
    '\.(jpe?g|png|gif|tiff?|p[abgp]m|svg)$': ['gpicview'],
    '\.(pax|cpio|zip|jar|ar|xar|rpm|7z)$': ['tar', 'tf'],
    '\.(tar\.|t)(z|gz|bz2?|xz)$': ['tar', 'tf'],
    '\.(mp4|mkv|avi|flv|mpg|movi?|m4v|webm)$': ['mpv']
}
othertypes = {'dir': ['rox'], 'txt': ['gvim', '--nofork']}

def main(argv):
    """Entry point for this script.

    Arguments:
        argv: command line arguments; list of strings.
    """
    if argv[0].endswith(('open', 'open.py')):
        del argv[0]
    opts = argparse.ArgumentParser(prog='open', description=__doc__)
    opts.add_argument('-v', '--version', action='version',
                      version=__version__)
    opts.add_argument('-a', '--application', help='application to use')
    opts.add_argument('--log', default='warning',
                      choices=['debug', 'info', 'warning', 'error'],
                      help="logging level (defaults to 'warning')")
    opts.add_argument("files", metavar='file', nargs='*',
                      help="one or more files to process")
    args = opts.parse_args(argv)
    logging.basicConfig(level=getattr(logging, args.log.upper(), None),
                        format='%(levelname)s: %(message)s')
    logging.info('command line arguments = {}'.format(argv))
    logging.info('parsed arguments = {}'.format(args))
    fail = "opening '{}' failed: {}"
    for nm in args.files:
        logging.info("Trying '{}'".format(nm))
        if not args.application:
            if isdir(nm):
                cmds = othertypes['dir'] + [nm]
            elif isfile(nm):
                cmds = matchfile(filetypes, othertypes, nm)
            else:
                cmds = None
        else:
            cmds = [args.application, nm]
        if not cmds:
            logging.warning("do not know how to open '{}'".format(nm))
            continue
        try:
            Popen(cmds)
        except OSError as e:
            logging.error(fail.format(nm, e))
    else:  # No files named
        if args.application:
            try:
                Popen([args.application])
            except OSError as e:
                logging.error(fail.format(args.application, e))

def matchfile(fdict, odict, fname):
    """For the given filename, returns the matching program. It uses the `file`
    utility commonly available on UNIX.

    Arguments:
        fdict: Handlers for files. A dictionary of regex:(commands)
            representing the file type and the action that is to be taken for
            opening one.
        odict: Handlers for other types. A dictionary of str:(arguments).
        fname: A string containing the name of the file to be opened.

    Returns: A list of commands for subprocess.Popen.
    """
    for k, v in fdict.items():
        if search(k, fname, IGNORECASE) is not None:
            return v + [fname]
    try:
        if b'text' in check_output(['file', fname]):
            return odict['txt'] + [fname]
    except CalledProcessError:
        logging.warning("the command 'file {}' failed.".format(fname))
        return None

if __name__ == '__main__':
    main(argv)

---

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