为什么 python 找不到我安装的库？

Question

I use python 3.9 and it is no longer able to find the libraries that I have installed libaries even though they are installed.

When I for example import pandas I get this message,

>>> import pandas
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    import pandas
ModuleNotFoundError: No module named 'pandas'

When I use pip to install the library it tells me that it already has been installed.

C:\Users\malth>pip install pandas
Requirement already satisfied: pandas in c:\users\malth\appdata\local\programs\python\python39\lib\site-packages (1.2.3)
Requirement already satisfied: python-dateutil>=2.7.3 in c:\users\malth\appdata\local\programs\python\python39\lib\site-packages (from pandas) (2.8.1)
Requirement already satisfied: pytz>=2017.3 in c:\users\malth\appdata\local\programs\python\python39\lib\site-packages (from pandas) (2021.1)
Requirement already satisfied: numpy>=1.16.5 in c:\users\malth\appdata\local\programs\python\python39\lib\site-packages (from pandas) (1.20.1)
Requirement already satisfied: six>=1.5 in c:\users\malth\appdata\local\programs\python\python39\lib\site-packages (from python-dateutil>=2.7.3->pandas) (1.15.0)

I can even see the library in the site-packages folder.

Answer 1

Try creating virtual environment, configure it and then install whatever module you require. Its the most easiest way to skip module error anytime.

Answer 2

Try to do pip --version . If you have a multiple pythons on your pc, you might have a pip that linked to another version. I guess you should try to use pyenv or virtualenv . This modules allowed you to avoid situation which I described above. Also it's a good practice to keep you python env isolated for a specific project.

Answer 3

As N.Singh has suggested, I would try to set up a new conda environment, adding all possible packages or libraries you will use and then I will make it active. Information about it can be found here: https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html#activating-an-environment . I really hope this helps. I have already had the same problem few months ago and worked for me.