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Introduction to Python
Prof. Dr. Gerit Wagner
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Projekt: Einführung in Python (1)

Project: Groups, forks and setup

  • Groups formed in the issue feeds
  • Forks were created. Note: we added best practices for forks: slide-33
  • Further questions related to the GitHub setup?
  • Setup completed?

Learning objectives:

  • Familiarize with Python syntax
  • Learn good debugging and development practices
  • Understand how to extend a Python package (CoLRev)

Groups

  • Form groups of three to four, discuss your solutions, and solve problems together.

Python

  • Supports multiple paradigms: object-oriented, procedural, or functional
  • Python is an interpreted language: no need to compile (build jars) before running
  • Uses indentation instead of brackets to separate blocks (such as if statements)
  • Is strongly, dynamically typed
  • Provides access to many packages on PyPI, covering machine learning, data science, web scraping, etc.
  • Python is actively developed with new versions introducing changes in functionality and old versions no longer receiving security updates

Overview

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Writing and running Python code

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Python packages

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For the tutorial, we switch to the tutorial_2024_04 branch:

git clone https://github.com/CoLRev-Environment/colrev
cd colrev
pip install -e .[dev]
git fetch
git checkout tutorial_2024_04
git reset --hard ca9902e666518af1d33a368adf055c9809004433
  • As the session progresses, you can checkout the current commits.
  • Whenever you see a git reset --hard ... command on the following slides, you can use it to set your repository to the required state (commit).

Python packages: Setting up entrypoints

We implement a simple version of CoLRev that should be available through a separate command:

colrev run
  • Check the last commit and the changes that were introduced. Which function does our new run command call?
  • Create the run module (module: file containing Python code) and the function that should be called. The function should print Start simple colrev run. Note that calling colrev.ops.run.main() means that colrev will try to import and run the main() function in the colrev/ops/run.py module. Check the other functions in the ui_cli/cli.py and the other modules in the colrev/colrev directory if necessary.
  • Create a commit once the command works.

Overview

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Data types

Dictionaries are efficient data structures, which can be used to handle bibliographic records, such as the following (in BibTex format):

@article{Pare2023,
  title   = {On writing literature reviews},
  author  = {Pare, Guy},
  journal = {MIS Quarterly},
  year    = {2023}
}

Create a dictionary containing these data fields and print it when colrev run is called.

Note: You can find the syntax for Python dictionaries (and many other data types) in the W3School.

Changing data

Next, we need a field indicating the record's status throughout the process.

Add a colrev_status field to the dictionary, and set its value to md_imported. Create a commit once the command prints the following:

Start simple colrev run
{'ID': 'Pare2023', 'title': 'On writing literature reviews', 'journal': 'MIS Quarterly', 'year': '2023', 'author': 'Pare, Guy', 'colrev_status': 'md_imported'}

$\hspace{8cm}$

To checkout the solution, run:

git reset --hard 6eb40fe1ac3a21c9be1b4d891525b6c5d78719f3

Overview

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Finding and adding external libraries

Next, we decide to load (parse) a BibTeX file stored in the project. Search for an appropriate Python library to parse BibTeX files. Try to figure out how to install it and how to use it.

We decide to use the BibtexParser package, which developed actively and available under an Open-Source license.

To install it, we could follow the instructions and run

pip install bibtexparser

To add it as a dependency of CoLRev and make it available for users of the CoLRev package, we run

poetry add bibtexparser

Check the changes and create a commit.

To checkout the solution, run:

git reset --hard 6b357d3cc5838e1c29ca908e5470dfd36335b9a2
pip install -e .[dev]

Using external libraries

Go to the bibtexparser tutorial and figure out how to load a BibTeX file (important : use v1!). An example records.bib file is available here.

Instead of defining the dictionary in the run.py, use the bibtexparser to load the records.bib file. Remember to store the records.bib in the project directory.

Afterwards, loop over the records (for ...) and print the title of each record.

Create a commit, and try to resolve linting errors (if any). We will address the typing-related issues together.

To checkout the solution, run:

git reset --hard ff2a044d2d0e535ea8814d31c962eae4eee64075

Next, we would like to create a function, which adds the journal_impact_factor based on the following table:

journal journal_impact_factor
MIS Quarterly 8.3
Information & Management 10.3

Add your changes to the staging area, run the pre-commit hooks, and address the warnings:

pre-commit run --all

To checkout the solution, run:

git reset --hard def8cd6113b9a7ded7a0d6abfd828c7735373197

Best practices

  • Carefully read tutorials, vignettes, and code examples (e.g., on GitHub)
  • Start with small code segments, try whether they work, and extend them
  • Add or commit working code frequently
  • Use code linters to ensure high code quality (run pre-commit run --all)
  • To debug code, check whether variables have the expected values (use assert statements)
  • When exceptions are thrown, read the Traceback:

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Next steps

  • Read the package development documentation.
  • Study code of related CoLRev packages.
  • Take notes on the CoLRev-objects or libraries that will be needed.

Tip: You can use this tutorial for more insights in Python