Creating "virtualenv" for an existing project

Question

I have a python on which I've been working on. Now I've realized that I need a virtual environment for it. How can I create it for an existing project? If I do this:

 virtualenv venv

will it work fine? Or do I have to re-create my project, create virtualenv and then copy the existing files to it?

Your project should provide `requirement.txt` for deployment. — Kir Chou, Jan 19 '17 at 16:08
Possible duplicate of [Comprehensive beginner's virtualenv tutorial?](http://stackoverflow.com/questions/5844869/comprehensive-beginners-virtualenv-tutorial) — Alexander Tyapkov, Jan 19 '17 at 16:12

score 18 · Accepted Answer · answered Jan 19 '17 at 16:10

18

You can just create an virtual enviroment with virtualenv venv and start it with venv/bin/activate.
You will need to reinstall all dependencies using pip, but the rest should just work fine.

answered Jan 19 '17 at 16:10

BigZ

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Can you provide some more information about `virtualenv venv`? Does that create a `venv` directory in the current shell path or does it create it somewhere in the global filesystem? – alex Jun 08 '18 at 13:31
@BigZ Is there a way to do so with virtualenvwrapper? mkvirtualenv? – hamza keurti Jun 22 '18 at 15:17
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For me it worked with `source venv/bin/activate` rather than what is there. – Homero Esmeraldo Jan 23 '19 at 17:00
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@alex I just tested it and the venv folder is created in the directory where the command `virtualenv venv` is run. – Homero Esmeraldo Jan 23 '19 at 17:03
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For me to activate the venv the command was: venv/Scripts/activate – Anshuman Kirty Nov 27 '20 at 06:29

9000 · Answer 2 · 2018-01-10T17:34:26.657

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The key thing is creating requirements.txt.

Create a virtualenv as normal. Do not activate it yet.

Now you need to install the required packages. If you do not readily remember it, ask pip:

pip freeze > requirements.txt

Now edit requirements.txt so that only the packages you know you installed are included. Note that the list will include all dependencies for all installed packages. Remove them, unless you want to explicitly pin their versions, and know what you're doing.

Now activate the virtualenv (the normal source path/to/virtualenv/bin/activate).

Install the dependencies you've collected:

pip install -r requirements.txt

The dependencies will be installed into your virtualenv.

The same way you'll be able to re-create the same env on your deployment target.

edited Jan 10 '18 at 17:34

answered Jan 19 '17 at 16:16

9000

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why so difficult? why not create virt env, activate it and freeze the requirements? – Gaji Jan 19 '17 at 16:20
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because a new virtual environment won't have the libraries you had previously installed. `pip freeze` the requirements first, then create a new environment, activate it and then `pip install -i requirements.txt`. The last command will run `pip` from the new virtual environment and the libraries thus installed will not be available when you deactivate that virtual environment to work on something else... – rtkaleta Jan 19 '17 at 16:24
I also recommend the excellent [virtualenvwrapper](https://virtualenvwrapper.readthedocs.io). Then, you can `mkvirtualenv `, `workon ` and `deactivate` to get around - which IMHO is much easier to remember. – rtkaleta Jan 19 '17 at 16:27
This steps are giving me same errors (but for another libriary) as from here https://stackoverflow.com/questions/28167987/python-pip-trouble-installing-from-requirements-txt – Carmine Tambascia May 18 '18 at 11:17

score 9 · Answer 3 · answered Jan 24 '20 at 11:50

If you are using from windows then follow the following procedure:

Step 1: Go to your root directory of existing python project

Step 2: Create virtual environment with virtualenv venv

Step 4: Go to /Scripts and type this command activate

then if you would like to install all required library , pip3 install -r requirements.txt

score 0 · Answer 4 · answered Sep 27 '22 at 09:01

There is something that I would like to add to this question. Because, newbees always have a problem and even once in a while, I do some mistake like that.

If you do not have requirements.txt for an already existing python-project, then you are doomed. Save at-least 2-3 hours of the day to recover the requirements.txt for an already existing python-project.

The best way to see it through and only if you are lucky, remember from that python-project, the most import package. By most-important, I mean the package that has highest-dependency.
Once, you have located this highest-dependency package, install it via pip. This will install all the dependency of the highest dependency package.

Now, see if it works. If it does, Voila !! If it doesn't you will have get where the conflicts are and start to resolve them one-by-one.

I was working on such a situation recently, where there was no requirements.txt. But I knew, the highest dependency was this deep-learning package called Sentence-Transformers and I installed it and with minor conflicts, resolved everything.

Best-of-luck !! Let me know if it ever helped anyone !!

Creating "virtualenv" for an existing project

4 Answers4