Can I import default Python modules in a Python Docker image?-CodePudding

I am new to Docker, and as a learning exercise, I want to make a custom Python package available through a Docker image. The package is called hashtable-nicolerg and includes a HashTable class that can be imported with from hashtable_nicolerg.hashtable import HashTable.

It is straightforward to create an image with additional Python packages installed:

Write a Dockerfile

# Dockerfile
FROM python:3
RUN pip install --no-cache-dir hashtable-nicolerg

Build the image
```
docker build -t python-hashtable .
```

However, the goal, which I realize is hardly an abundant use-case for Docker images, is for the user to be able to create HashTable instances as soon as the container's Python prompt starts.

Specifically, this is the current behavior:

$ docker run -it python-hashtable
Python 3.11.0 (main, Nov 15 2022, 19:58:01) [GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> hash_table = HashTable(capacity=100)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'HashTable' is not defined
>>> from hashtable_nicolerg.hashtable import HashTable
>>> hash_table = HashTable(capacity=100)

And this is the desired behavior:

$ docker run -it python-hashtable
Python 3.11.0 (main, Nov 15 2022, 19:58:01) [GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> hash_table = HashTable(capacity=100)

I don't want my imaginary users to have to type from hashtable_nicolerg.hashtable import HashTable every time they run a container from this image. So, is it possible for me to effectively run from hashtable_nicolerg.hashtable import HashTable within my Docker image so that users don't have to manually import this module?

Again, I realize this is not the most popular use-case for a Docker image. I'm using this as an exercise to learn more about Python and Docker. I'd appreciate any help!

CodePudding user response：

If the PYTHONSTARTUP environment variable exists and is the name of a valid Python file, then that file will be executed when any new Python shell starts up.

So whether you want to do this in a Docker container or on your local machine, it works the same way. Define PYTHONSTARTUP (in .bashrc, for instance) and then write a startup file.

# .bashrc
export PYTHONSTARTUP=~/.python_startup

# .python_startup
from hashtable_nicolerg.hashtable import HashTable

CodePudding user response：

Thanks to Silvio Mayolo for the answer! Here is a Docker alternative to exporting an environment variable from ~/.bashrc:

# Dockerfile
FROM python:3
RUN pip install --no-cache-dir hashtable-nicolerg

WORKDIR /
COPY .python_startup .
ENV PYTHONSTARTUP=./.python_startup

Then after building the image with docker build -t python-hashtable ., I get the desired behavior:

$ docker run -it python-hashtable
Python 3.11.0 (main, Nov 15 2022, 19:58:01) [GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> hash_table = HashTable(capacity=100)