How can I use a Python script in the command line without cd-ing to its directory? Is it the PYTHONPATH?
Question:
How can I make any use of PYTHONPATH? When I try to run a script in the path the file is not
found. When I cd to the directory holding the script the script runs. So what good is the
PYTHONPATH?
$ echo $PYTHONPATH
:/home/randy/lib/python
$ tree -L 1 '/home/randy/lib/python'
/home/randy/lib/python
├── gbmx_html.py
├── gbmx.py
├── __init__.py
├── __pycache__
├── scripts
└── yesno.py
$ python gbmx.py -h
python: can't open file 'gbmx.py': [Errno 2] No such file or directory
$ cd '/home/randy/lib/python'
After cd to the file directory it runs ..
$ python gbmx.py -h
usage: gbmx.py [-h] [-b]
Why can I not make any use of the PYTHONPATH?
Answers:
You’re confusing PATH and PYTHONPATH. You need to do this:
export PATH=$PATH:/home/randy/lib/python
PYTHONPATH is used by the python interpreter to determine which modules to load.
PATH is used by the shell to determine which executables to run.
I think you’re a little confused. PYTHONPATH sets the search path for importing python modules, not for executing them like you’re trying.
PYTHONPATH Augment the default search path for module files. The
format is the same as the shell’s PATH: one or more directory
pathnames separated by os.pathsep (e.g. colons on Unix or semicolons
on Windows). Non-existent directories are silently ignored.
In addition to normal directories, individual PYTHONPATH entries may
refer to zipfiles containing pure Python modules (in either source or
compiled form). Extension modules cannot be imported from zipfiles.
The default search path is installation dependent, but generally
begins with prefix/lib/pythonversion (see PYTHONHOME above). It is
always appended to PYTHONPATH.
An additional directory will be inserted in the search path in front
of PYTHONPATH as described above under Interface options. The search
path can be manipulated from within a Python program as the variable
sys.path.
http://docs.python.org/2/using/cmdline.html#envvar-PYTHONPATH
What you’re looking for is PATH.
export PATH=$PATH:/home/randy/lib/python
However, to run your python script as a program, you also need to set a shebang for Python in the first line. Something like this should work:
#!/usr/bin/env python
And give execution privileges to it:
chmod +x /home/randy/lib/python/gbmx.py
Then you should be able to simply run gmbx.py from anywhere.
PYTHONPATH only affects import statements, not the top-level Python interpreter’s lookup of python files given as arguments.
Needing PYTHONPATH to be set is not a great idea – as with anything dependent on environment variables, replicating things consistently across different machines gets tricky. Better is to use Python ‘packages’ which can be installed (using ‘pip’, or distutils) in system-dependent paths which Python already knows about.
Have a read of https://the-hitchhikers-guide-to-packaging.readthedocs.org/en/latest/ – ‘The Hitchhiker’s Guide to Packaging’, and also http://docs.python.org/3/tutorial/modules.html – which explains PYTHONPATH and packages at a lower level.
I think you’re mixed up between PATH and PYTHONPATH. All you have to do to run a ‘script’ is have it’s parental directory appended to your PATH variable. You can test this by running
which myscript.py
Also, if myscripy.py depends on custom modules, their parental directories must also be added to the PYTHONPATH variable. Unfortunately, because the designers of python were clearly on drugs, testing your imports in the repl with the following will not guarantee that your PYTHONPATH is set properly for use in a script. This part of python programming is magic and can’t be answered appropriately on stackoverflow.
$python
Python 2.7.8 blahblahblah
...
>from mymodule.submodule import ClassName
>test = ClassName()
>^D
$myscript_that_needs_mymodule.submodule.py
Traceback (most recent call last):
File "myscript_that_needs_mymodule.submodule.py", line 5, in <module>
from mymodule.submodule import ClassName
File "/path/to/myscript_that_needs_mymodule.submodule.py", line 5, in <module>
from mymodule.submodule import ClassName
ImportError: No module named submodule
With PYTHONPATH set as in your example, you should be able to do
python -m gmbx
-m option will make Python search for your module in paths Python usually searches modules in, including what you added to PYTHONPATH. When you run interpreter like python gmbx.py, it looks for particular file and PYTHONPATH does not apply.
How can I make any use of PYTHONPATH? When I try to run a script in the path the file is not
found. When I cd to the directory holding the script the script runs. So what good is the
PYTHONPATH?
$ echo $PYTHONPATH
:/home/randy/lib/python
$ tree -L 1 '/home/randy/lib/python'
/home/randy/lib/python
├── gbmx_html.py
├── gbmx.py
├── __init__.py
├── __pycache__
├── scripts
└── yesno.py
$ python gbmx.py -h
python: can't open file 'gbmx.py': [Errno 2] No such file or directory
$ cd '/home/randy/lib/python'
After cd to the file directory it runs ..
$ python gbmx.py -h
usage: gbmx.py [-h] [-b]
Why can I not make any use of the PYTHONPATH?
You’re confusing PATH and PYTHONPATH. You need to do this:
export PATH=$PATH:/home/randy/lib/python
PYTHONPATH is used by the python interpreter to determine which modules to load.
PATH is used by the shell to determine which executables to run.
I think you’re a little confused. PYTHONPATH sets the search path for importing python modules, not for executing them like you’re trying.
PYTHONPATH Augment the default search path for module files. The
format is the same as the shell’s PATH: one or more directory
pathnames separated by os.pathsep (e.g. colons on Unix or semicolons
on Windows). Non-existent directories are silently ignored.In addition to normal directories, individual PYTHONPATH entries may
refer to zipfiles containing pure Python modules (in either source or
compiled form). Extension modules cannot be imported from zipfiles.The default search path is installation dependent, but generally
begins with prefix/lib/pythonversion (see PYTHONHOME above). It is
always appended to PYTHONPATH.An additional directory will be inserted in the search path in front
of PYTHONPATH as described above under Interface options. The search
path can be manipulated from within a Python program as the variable
sys.path.
http://docs.python.org/2/using/cmdline.html#envvar-PYTHONPATH
What you’re looking for is PATH.
export PATH=$PATH:/home/randy/lib/python
However, to run your python script as a program, you also need to set a shebang for Python in the first line. Something like this should work:
#!/usr/bin/env python
And give execution privileges to it:
chmod +x /home/randy/lib/python/gbmx.py
Then you should be able to simply run gmbx.py from anywhere.
PYTHONPATH only affects import statements, not the top-level Python interpreter’s lookup of python files given as arguments.
Needing PYTHONPATH to be set is not a great idea – as with anything dependent on environment variables, replicating things consistently across different machines gets tricky. Better is to use Python ‘packages’ which can be installed (using ‘pip’, or distutils) in system-dependent paths which Python already knows about.
Have a read of https://the-hitchhikers-guide-to-packaging.readthedocs.org/en/latest/ – ‘The Hitchhiker’s Guide to Packaging’, and also http://docs.python.org/3/tutorial/modules.html – which explains PYTHONPATH and packages at a lower level.
I think you’re mixed up between PATH and PYTHONPATH. All you have to do to run a ‘script’ is have it’s parental directory appended to your PATH variable. You can test this by running
which myscript.py
Also, if myscripy.py depends on custom modules, their parental directories must also be added to the PYTHONPATH variable. Unfortunately, because the designers of python were clearly on drugs, testing your imports in the repl with the following will not guarantee that your PYTHONPATH is set properly for use in a script. This part of python programming is magic and can’t be answered appropriately on stackoverflow.
$python
Python 2.7.8 blahblahblah
...
>from mymodule.submodule import ClassName
>test = ClassName()
>^D
$myscript_that_needs_mymodule.submodule.py
Traceback (most recent call last):
File "myscript_that_needs_mymodule.submodule.py", line 5, in <module>
from mymodule.submodule import ClassName
File "/path/to/myscript_that_needs_mymodule.submodule.py", line 5, in <module>
from mymodule.submodule import ClassName
ImportError: No module named submodule
With PYTHONPATH set as in your example, you should be able to do
python -m gmbx
-m option will make Python search for your module in paths Python usually searches modules in, including what you added to PYTHONPATH. When you run interpreter like python gmbx.py, it looks for particular file and PYTHONPATH does not apply.