riff Sample: Shell Python2 Uppercase

A sample function that uppercases the input text using Python. Unlike the traditional shell invoker, this sample also installs Python and is implemented in Python instead of shell.

Deployment

1. Setup a running riff install (tested with riff 0.0.4)

   See riff's Getting Started guide. Skip if you already have riff running.

2. Clone this repo

   git clone https://github.com/projectriff-samples/shell-python2-uppercase.git
   cd shell-python2-uppercase

3. Initialize the function definition

   Since there are multiple files in the directory, we need to tell riff which file to use.

   riff init -a uppercase.sh

4. Install Python

   The shell-function-invoker does not have Python installed by default. We can copy Python from another Docker image.

   Add this line to the Dockerfile generated by riff init after the FROM command:

   COPY --from=python:2.7-alpine /usr/local /usr/local
   

   Resulting in a Dockerfile like:

   FROM projectriff/shell-function-invoker:latest
   COPY --from=python:2.7-alpine /usr/local /usr/local
   ARG FUNCTION_URI="/uppercase.sh"
   ADD uppercase.sh /
   ENV FUNCTION_URI $FUNCTION_URI
   

   NOTE: The script has a .sh file extension even though the content is Python. If you'd like to rename uppercase.sh to uppercase.py make sure to also update references in the Dockerfile.

5. Deploy the function to riff

   riff update

6. Invoke the function

   riff publish -d hello -r

   Resulting in:

   Posting to http://127.0.0.1:31970/requests/shell-python2-uppercase
   HELLO
   

How it works

The riff shell-function-invoker executes an arbitrary file. While a shell script is most common, any executable file will work.

The first line of uppercase.sh is a shebang which instructs the system how to interpret the file. In this case we tell the interpreter that the rest of the file is Python.

#!/usr/bin/env python2

But Python isn't available within the shell-function-invoker container by default. We install Python to the container by copying the bits from another Docker image that has Python installed, in this case python:2.7-alpine.

COPY --from=python:2.7-alpine /usr/local /usr/local

You can be more precise with the exact version of Python or upgrade to Python3 by changing the version number of the Docker container the bits are copied from.

The script itself consumes standard input, converts the test to uppercase and prints to standard output.

for line in fileinput.input():
    sys.stdout.write(line.upper())

When the input stream ends, the script exits.