I am doing maintenance for a python code. Python is installed in /usr/bin, the code installed in /aaa, a python 2.5 installed under /aaa/python2.5. Each time I run Python, it use /usr/bin one. How to make it run /aaa/python2.5?
Also when I run Python -v; import bbb; bbb.__file__; it will automatically show it use bbb module under /usr/ccc/(don't know why), instead of use bbb module under /aaa/python2.5/lib
How to let it run python2.5 and use `/aaa/python2.5/lib' module? The reason I asking this is if we maintain a code, but other people is still using it, we need to install the code under a new directory and modify it, run it and debug it.
Change the shebang-line (if there is such a line)
Nomally
#!/usr/bin/env python
is used to start the python interpreter first found in the path, this is how virtualenv works, i.e. it changes the path so that the chosen interpreter is placed first and the line above simply works.
In your example, change i to
#!/aaa/python2.5
Note that the executable-flag has to be set for this to work.
Example:
$ chmod u+x script.py
$ ./script.py
See PYTHONPATH for a description of how python searches for modules.
Do /aaa/python2.5 python_code.py. If you use Python 2.5 more often, consider changing the $PATH variable to make Python 2.5 the default.
Add this to your .bash_profile file (create if non exist, it's a hidden file):
python25(){
/aaa/python2.5 "$1"
}
Now you can use Python (latest) and Python 2.5:
$ python my_file.py
$ python25 my_file.py
Good luck!
Related
Suppose that I have a Python file named
test.py
and I want to be able to run it with different versions of python installed in my computer.
I know this can be done for example:
To run it with my version of Python2.x:
py -2 test.py
To run it with my version of Python3.x:
py -3 test.py
I would like to edit the way this command is written, in order to:
Use Python2.x with
python2 test.py
Use Python3.x with
python3 test.py
I guess I have to edit some system variables, but I am not quite sure which and I don't want to mess up anything. I am using Windows10. Anybody has any idea?
You can run your script by specifying the path for your specific python version like so: c:\python\2.5\python.exe test.py.
You can also create environment variables for each version manually if you'd like to. Create and modify environment variables Windows 10
I have installed Anaconda 2 & 3 in my system. Anaconda 2 contains python 2.7 & Anaconda 3 contains python 3.6.
I need to run my python code using command prompt & I need to use python 3.6
While I'm running python --version, I'm getting python 2.7.14. How do I change it to python 3.6?
As you can see, I have both Python2 and Python3 installed.
I hope you know that the path of the python executable has to be added to the PATH environment variable in Windows. As you can see, the path of Python2 is placed above the path of Python3 in my system.
How does the cmd run commands?
It searches for an executable with the same name in the directory the cmd has been opened in, then goes and searches for the command in the locations provided in the Windows PATH variable, from TOP to BOTTOM.
Which means, it gets the path to Python2 before it can get to the path of Python3. Therefore, every time you type python in your cmd, it runs Python2.
Both Python2 and Python3 executables have the same name in Windows so it never runs python3.
What seems like an obvious solution?
You might think, changing the name of python.exe to python3.exe for the Python3 executable will solve your problem. You are partially right, it will work. But you have to use python3 file.py or python3 --version, which I think, is understandable. But, pip will no longer work if you change the name of the original python executable. You will no longer be able to install external packages and modules.
How can this problem be solved?
You can create an alias for the Python3 executable called python3.bat.
.exe and .bat files can be called from the cmd directly without using their extension. We always write python filename.py instead of python.exe filename.py although both are correct. The same can be done with .bat files.
Go back to the first image and notice the python3.bat file below python.exe. That is my way of calling python3 without renaming my original python executable.
python3.bat
Create a new file using notepad or something and paste this %~dp0python %*
I don't fully understand how this works except that dp0 basically runs python from inside the same directory and %* passes all the arguments to the python executable. Place this file inside your Python3 installation directory and your problem will hopefully be solved.
python3 basically runs your python3.bat file, which in turn runs the python.exe from its folder and passes the arguments to it.
I hope this solves your problem.
You should have python3 also in your path. You could use python3 to run your script:
python3 <your_script>
But to answer your question, you could use alias and update it as python.
$ python --version
Python 2.7.6
$ alias python=python3
$ python --version
Python 3.6.4
If you want to run Python 3.6, then execute python3.6.
Otherwise, check with which python where the symbolic link to the actual python executable is. On my system, it's
/usr/bin/python
and when I ls -la /usr/bin/python, it gives
lrwxrwxrwx 42 user user 42 Aug 24 03:45 /usr/bin/python -> python2.7
If you are really sure that you want to do it, you can now just move the old symlink somewhere:
sudo mv /usr/bin/python /usr/bin/old_python
and create a new symlink:
sudo ln -s /usr/bin/python3.6 /usr/bin/python
Now you should get something like:
$ python --version
Python 3.6.5
I don't guarantee that it doesn't break everything in the world, especially if you have some distro that has a package manager that relies on a specific python version under python.
This seemed to work nicely on Linux Mint 18.
I made a small trick to solve this problem. For me
C:\Python27
and
C:\Python27\Scripts
were at the top of the PATH Environment variable list. I simply selected them and clicked on Moved Down to shift them to the end of the list.
Just make sure that your path of Python3 and its Script folder is above Python2 path.
And it solved the problem for me. Hope it would help you too.
Reason :
How does the cmd run commands?
It searches for an executable with the same name in the directory the cmd has been opened in, then goes and searches for the command in the locations provided in the Windows PATH variable, from TOP to BOTTOM. Which means, it gets the path to Python2 before it can get to the path of Python3. Therefore, every time you type python in your cmd, it runs Python2.
Both Python2 and Python3 executables have the same name in Windows so it never runs python3.
reason is taken from the accepted answer to this question.
In order to run your script with python 3 you can use
python3 <path to file>
P.S.: this should be a comment, but I do not have the required reputation. :)
If Anaconda 3's is the only python3 interpreter in the system you can run python3 instead of python in your command line and it should work.
You can alter PATH parameter inverting the positions of both interpreters.
I have two versions of the python which the first path is python 2(I am still working with python 2), but there are some scripts which should use python 3. This is what I have done:
I have create a bat file.
ex:
open Notepad++ and write :
#echo off
set PYTHONPATH=
"%~dpn0.py" %*
save it as 'yourscriptname.cmd'.
before my script(which should use python3) I just run this file in command line and then run my script. it is working.
I have 2 versions of python installed on my server.
Python 2.6 in /usr/bin/python
Python 2.7.8 in /usr/src
Python 2.7.8 install guide
How do I make python scripts use 2.7.8? instead of 2.6?
how do I set up an alias?
Thanks
Write:
#!<path to your python interpreter>
as the first line of the script your run. Then just execute it.
Other option:
<path to your python interpreter> your_script.py
There are multiple ways of doing this. First, I would suggest you check your $PATH environment variable to see if it holds the path to both of your python versions. If it doesn't, you can either add the path or simply make a symlink to it from /usr/bin/ and call it python2.7, for example.
Then you can use #Pavel's suggestion of specifying the path to the interpreter in the shebang of the file.
If you followed my previous instructions, your shebang should look something similar to the following.
#!/usr/bin/env python2.7
You could also use the second way #Pavel showed you, by simply calling the interpreter first in the terminal and pointing it to the script.
/usr/bin/python2.7 my_script.py
The best option you have, which I recommend, is using virtualenv as suggested before, but only if you want it for specific scripts. If you want it globally, I would suggest you read further.
Finally, if you want all your scripts to run under python 2.7 then I suggest you remove python 2.6 and install the 2.7 version from the package manager, the right way, and save yourself a lot of hassle.
I recently installed epd python distribution in ubuntu. This got installed in the folder /home/jai/Downloads/epd_free-7.3-2-rh5-x86_64
Can you tell me how to make this python as my default python?
I get errors while running a test program (it seems my default python is different and it doesn't have numpy library, other libraries that come along epd python distribution.)
My test program is here: http://www.southampton.ac.uk/~fangohr/computing/download/python/tests/testall.py
The "default" python depends on how you're invoking it.
On Ubuntu, python is normally installed as /usr/bin/python (not /bin/python) -- which may be a symbolic link.
If you invoke the python command, e.g.:
$ python myscript.py
it will use whichever python executable is in a directory that appears first in your $PATH. You can modify your $PATH, either for your current shell:
export PATH="/some/dir:$PATH"
or for all future shells by updating your $HOME/.bashrc, $HOME/.bash_profile, or whatever. /usr/local/bin is one common place to put system-specific executables, or $HOME/bin for user-specific executables.
If you want to execute the script itself, you'll need a shebang as the first line of the script:
$ head -1 myscript.py
#!/usr/bin/python
$ ./myscript.py
...
You can edit the shebang to refer to whatever Python executable you want to use.
You can replace /usr/bin/python with your preferred Python executable, but that might cause unwanted side effects; existing Python scripts that assume /usr/bin/python is the default might break.
Another option is to change the shebang to:
#!/usr/bin/env python
which lets you execute the script directly while still using whichever python is first in your $PATH. This may or may not be a good idea; see my answer to this question for further discussion.
Default python is the one found in /usr/bin directory with the name python. Making a symbolic link of :
ln -s /home/jai/Downloads/epd_free-7.3-2-rh5-x86_64 /usr/bin/python
Assuming that is the name of the python executable, not the installer. After you installed, use the path where you installed it. f.e /home/iai/myNewPythonInstallation
might do the trick.
Most likely default 2.7 python is occupying that name, so you need to remove that, or use another name like epdPython. Then running python scripts would happen with:
epdPython myscript.py
I am debugging some python code in emacs using pdb and getting some import issues. The dependencies are installed in one of my bespoked virtualenv environments.
Pdb is stubbornly using /usr/bin/python and not the python process from my virtualenv.
I use virtualenv.el to support switching of environments within emacs and via the postactivate hooks described in
http://jesselegg.com/archives/2010/03/14/emacs-python-programmers-2-virtualenv-ipython-daemon-mode/
This works well when running M-x python-shell
>>> import sys
>>> print sys.path
This points to all of my virtualenv libraries indicating that the python-shell is that of my virtualenv.
This is contradicted however by M-! which python, which gives /usr/bin/python
Does anyone know how I can tell M-x pdb to adopt the python process from the currently active virtualenv?
Invoke pdb like this:
python -m pdb myscript.py
Instead of
pdb myscript.py
python-shell uses variable python-default-interpreter to determine which python interpreter to use. When the value of this variable is cpython, the variables python-python-command and python-python-command-args are consulted to determine the interpreter
and arguments to use. Those two variables are manipulated by virtualenv.el to set the current virtual environment.
So when you use python-shell command, it uses your virtual environments without any problem.
But, when you do M-! python, you're not using the variables python-python-command and python-python-command-args. So it uses the python tools it finds in your path.
When you call M-x pdb it uses gud-pdb-command-name as the default pdb tool. To redefine this variable, each time you activate an environment, you could do something like this :
(defadvice virtualenv-activate (after virtual-pdb)
(custom-set-variables
'(gud-pdb-command-name
(concat virtualenv-active "/bin/pdb" ))))
(ad-activate 'virtualenv-activate)
To have pdb in your virtual environment, do the following :
cp /usr/bin/pdb /path/to/virtual/env/bin
Then edit the first line of /path/to/virtual/env/bin/pdb to have :
#! /usr/bin/env python
Reactivate your env and Pdb should now use your virtualenv python instead of the system-wide python.
Possibly, your pdb command is tied to a certain specific version.
$ ls -ald /usr/bin/pdb
lrwxrwxrwx 1 root root 6 Jun 2 23:02 /usr/bin/pdb -> pdb2.6
Then, look at the first line of pdb2.6. It contains
#! /usr/bin/python2.6
This is why pdb is stubborn and always seems to run under a specific version of Python. Because it really is! Actually, this sort of dependency makes sense for a piece of software like a symbolic debugger.
I've compiled python2.7 from sources and pdb is not there, apparently.
After some scrutiny, I found pdb.py for python-2.7, under the lib folder.
I've then created some symlinks to it, for convenience:
$ cd /opt/python-dev ##-- this is where I installed from sources
$ cd bin
$ sudo ln -s ../lib/python2.7/pdb.py pdb2.7
$ sudo ln -s pdb2.7 pdb
Now observe the first line of pdb2.7. It reads:
#! /usr/bin/env python
... which looks better than the previous version. It basically means that pdb will be launched under the current Python you have defined in your environment, whatever it is, instead of anything hardcoded, like /usr/bin/python or /usr/bin/python2.6 are. Good to know!
I've also removed pdb and pdb2.6 from system files, once I prefer to develop/debug inside virtualenv. Doing that, I will not be caught again by the same trick.
I hope it helps.
A quick work-around is to explicitly call the python interpreter in you virtual env.
M-x pdb, then:
path/to/your/virtualenv/python3 -m pdb your_source.py