How to pass command line arguments to Python Docker container?

Before understanding docker container parameters, we must understand python command line parameters and how developers access them. Command line arguments are very useful when we want to control a Python script outside of the program.

Access command line parameters of python script

Step 1: Create python script main.py

Example

# sys will allow us to access the passed arguments
import sys

# sys.argv[0] access the first argument passed that is the python script name
print("\nFile or Script Name is :", sys.argv[0])

# print arguments other than the file name
print("\nArguments passed:", end = " ")
for i in range(1, len(sys.argv)):
   print(sys.argv[i], end = " ")

# Lowercase operation on the passed arguments
for i in range(1, len(sys.argv)):
   print(sys.argv[i].lower(), end = " ")

Step 2: Run on Terminal with Parameters

#python3 main.py HELLO THIS IS TUTORIALSPOINT

Output

File or Script Name is : main.py
Arguments passed: HELLO THIS IS TUTORIALSPOINT
hello this is tutorialspoint

Pass these parameters to the docker container

We have different ways of passing command line arguments to docker containers. Some of them are mentioned step by step below.

Using Docker parameters with ENTRYPOINT

The trick is to use an entry point with a dockerfile and redirect that entry point to the python file for execution. After that, just pass the required python parameters during running the docker container.

Step 1: Create Dockerfile

Example

FROM python
WORKDIR /app
COPY . /app/
ENTRYPOINT ["python3", "main.py"]

Step 2: Build the image

Example

#docker build -t arg_py .

Output

Sending build context to Docker daemon 8.192kB
Step 1/4 : FROM python
---> fa9122485d1d
Step 2/4 : WORKDIR /app
---> Using cache
---> 9e9708fe1d43
Step 3/4 : COPY . /app/
---> aea9ecf32f55
Step 4/4 : ENTRYPOINT ["python3", "main.py"]
---> Running in 864440fa7988
Removing intermediate container 864440fa7988
---> d6e31e5606b8
Successfully built d6e31e5606b8
Successfully tagged arg_py:latest

Step 3: Run the container

#docker run --name mycontainer arg_py HELLO FROM TUTORIALSPOINT

Example

File or Script Name is : main.py
Arguments passed: HELLO FROM TUTORIALSPOINT
hello from tutorialspoint

Use Docker environment variables via ENTRYPOINT

The Docker run command provides us with some extraordinary features, one of which is environment variables. Here we will use these environment variables to pass data to the internal python script on the docker container.

Step 1: Create a python script to access environment variables

Creating the python script this time will be very similar to the first example. Instead of importing the "sys" module, we will import the "os" module to get environment variables. Create a python file and paste the following code.

Example

import os

#declare some variables for environment variable
#os.getenv will fetch the environment variables from the container.
userName = os.getenv("User_Name")
passWord = os.getenv("Pass_Word")

#Now print the variables that has been fetched.
print("Running with user: %s" % userName)
print("Your password: %s" % passWord)

#Apply some operation
print(userName.upper())
print(passWord.upper())

Save the above file as main.py

Step 2: Build dockerfile

Build the dockerfile to create a new image using this python code. This dockerfile is the same as the one we created before, just changed the python code in main.py.

Example

#docker build -t env_img .

Output

Sending build context to Docker daemon 3.072kB
Step 1/4 : FROM python
---> fa9122485d1d
Step 2/4 : WORKDIR /app
---> Using cache
---> 9e9708fe1d43
Step 3/4 : COPY . /app/
---> 31f98d53c161
Step 4/4 : ENTRYPOINT ["python3", "main.py"]
---> Running in bec1681a6842
Removing intermediate container bec1681a6842
---> 5dd89b0c7985
Successfully built 5dd89b0c7985
Successfully tagged env_img:latest

Step 3: Run the container

Use the environment variables mentioned in the python script during running the container. Docker run has a "-e" flag to mention any environment variable, we can mention multiple environment variables at once

Example

#docker run -e User_Name="TutorialsPoint" -e Pass_Word="secret" --name env_cont env_img

Output

Running with user: TutorialsPoint
Your password: secret
TUTORIALSPOINT
SECRET

This is how we pass command line arguments and environment variables to the python container running on the docker daemon with the help of docker client.

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