Module installs but cannot be imported

ghz 15hours ago ⋅ 5 views

I'm new to Python and I'm trying to run a Python2 script on a Mac that depends on a module, which I have installed but according to the script can't be found. Why is the following failing?

Home:Dev m$ python -V
Python 2.7.10
Home:Dev m$ sudo pip install coincurve==5.2.0 pysha3
Password:
The directory '/Users/m/Library/Caches/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/Users/m/Library/Caches/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Collecting coincurve==5.2.0
  Downloading coincurve-5.2.0-cp27-cp27m-macosx_10_6_intel.whl (157kB)
    100% |████████████████████████████████| 163kB 1.3MB/s 
Collecting pysha3
  Downloading pysha3-1.0.2.tar.gz (829kB)
    100% |████████████████████████████████| 829kB 692kB/s 
Requirement already satisfied: cffi>=1.3.0 in /usr/local/lib/python2.7/site-packages (from coincurve==5.2.0)
Requirement already satisfied: asn1crypto in /usr/local/lib/python2.7/site-packages (from coincurve==5.2.0)
Requirement already satisfied: pycparser in /usr/local/lib/python2.7/site-packages (from cffi>=1.3.0->coincurve==5.2.0)
Installing collected packages: coincurve, pysha3
  Running setup.py install for pysha3 ... done
Successfully installed coincurve-5.2.0 pysha3-1.0.2
Home:Dev m$ pip show coincurve
Name: coincurve
Version: 5.2.0
Summary: Cross-platform Python CFFI bindings for libsecp256k1
Home-page: https://github.com/ofek/coincurve
Author: Ofek Lev
Author-email: ofekmeister@gmail.com
License: MIT/Apache-2.0
Location: /usr/local/lib/python2.7/site-packages
Requires: cffi, asn1crypto
Home:Dev m$ python
Python 2.7.10 (default, Jul 15 2017, 17:16:57) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import coincurve
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named coincurve
>>>

Answer

The issue you're encountering arises because the pip command and the python command may not be referring to the same Python environment. When you run sudo pip install, you're installing the packages for the system's default Python environment, which is Python 2.7 in your case. However, when you run the python command, it may refer to a different Python environment that doesn't have access to the installed packages.

To troubleshoot and resolve this issue, follow these steps:

1. Check Which Python Version Is Used

First, let's confirm that the python and pip commands are referring to the same Python version.

  • Run the following commands:

    which python
which pip

    This will show you the paths for python and pip. They should both point to locations within the same Python installation.

  • If pip points to a different installation (e.g., a user installation like /Users/username/.local/), it might be installing packages for a different Python version, not the system's Python 2.7.

2. Ensure Correct pip for Python 2.7

You should make sure you're using pip associated with Python 2.7, especially when installing packages with sudo. The easiest way is to use pip2 instead of pip.

  • Install the packages using pip2:

    sudo pip2 install coincurve==5.2.0 pysha3

  • You can also verify pip2 points to the correct version:

    which pip2

3. Check Installed Packages in Python 2.7

After installing the packages, make sure that the Python interpreter is pointing to the correct site-packages directory:

  • Start Python 2.7 by running:

    python

  • Once inside the Python shell, check the module search path (sys.path):

    import sys
print(sys.path)

    Ensure that /usr/local/lib/python2.7/site-packages is included in the list of directories. This is where coincurve and pysha3 should have been installed.

  • If it's missing, you may need to adjust your Python environment or installation.

4. Using sudo Correctly

Sometimes, running sudo with pip might cause issues with permissions, as sudo can cause pip to install packages globally (and not for your user). You might want to use sudo -H to avoid this issue, as suggested by the warnings in your terminal:

sudo -H pip install coincurve==5.2.0 pysha3

5. Using Virtual Environments (Optional)

For managing dependencies more easily and avoiding issues with system-wide Python installations, it's a good practice to use virtual environments. This isolates your package installations from the system's Python environment.

  • You can create a virtual environment with virtualenv:

    sudo pip2 install virtualenv
virtualenv venv
source venv/bin/activate
pip install coincurve==5.2.0 pysha3

    Then, run your script inside the virtual environment, where the necessary modules will be available.

Conclusion:

  1. Ensure that python and pip are using the same Python environment (preferably Python 2.7 in your case).
  2. Use sudo -H pip to avoid permission issues when installing packages globally.
  3. Consider using a virtual environment for better package management and isolation from the system Python.

Let me know if you encounter any further issues!

#py