Repository

Repository is the main class of Pydriller, responsible of returning the list of commits you want. One of the main advantage of using PyDriller to mine software repositories is that it is highly configurable. We will now see all the options that once can pass to Repository.

Simple Scenario

This is the “Hello World” of Pydriller:

for commit in Repository("/Users/dspadini/myrepo").traverse_commits():
    print(commit.hash)

The function traverse_commits() of Repository will return the selected commits, in this simple case all of them. Now let’s see how we can customize Repository.

Selecting projects to analyze

The only required parameter of Repository is path_to_repo, which specifies the repo(s) to analyze. It must be of type str or List[str], meaning analyze only one repository or more than one.

Furthermore, PyDriller supports both local and remote repositories: if you pass an URL, PyDriller will automatically create a temporary folder, clone the repository, run the study, and finally delete the temporary folder.

For example, the following are all possible inputs for Repository:

# analyze only 1 local repository
url = "repos/pydriller/"

# analyze 2 local repositories
url = ["repos/pydriller/", "repos/anotherrepo/"]

# analyze both local and remote
url = ["repos/pydriller/", "https://github.com/apache/hadoop.git", "repos/anotherrepo"]

# analyze 1 remote repository
url = "https://github.com/apache/hadoop.git"

To keep track of what project PyDriller is analyzing, the Commit object has a property called project_name.

Selecting the Commit Range

By default, PyDriller analyzes all the commits in the repository. However, filters can be applied to Repository to visit only specific commits.

  • single (str): single hash of the commit. The visitor will be called only on this commit

FROM:

  • since (datetime): only commits after this date will be analyzed
  • from_commit (str): only commits after this commit hash will be analyzed
  • from_tag (str): only commits after this commit tag will be analyzed

TO:

  • to (datetime): only commits up to this date will be analyzed
  • to_commit (str): only commits up to this commit hash will be analyzed
  • to_tag (str): only commits up to this commit tag will be analyzed

ORDER:

  • order (str): one between ‘date-order’, ‘author-date-order’, ‘topo-order’, and ‘reverse’ (see this for more information). NOTE: By default, PyDriller returns the commits from the oldest to the newest. If you need viceversa instead (from the newest to the oldest), use “order=’reverse’”.

Examples:

# Analyze single commit
Repository('path/to/the/repo', single='6411e3096dd2070438a17b225f44475136e54e3a').traverse_commits()

# Since 8/10/2016
Repository('path/to/the/repo', since=datetime(2016, 10, 8, 17, 0, 0)).traverse_commits()

# Between 2 dates
dt1 = datetime(2016, 10, 8, 17, 0, 0)
dt2 = datetime(2016, 10, 8, 17, 59, 0)
Repository('path/to/the/repo', since=dt1, to=dt2).traverse_commits()

# Between tags
from_tag = 'tag1'
to_tag = 'tag2'
Repository('path/to/the/repo', from_tag=from_tag, to_tag=to_tag).traverse_commits()

# Up to a date
dt1 = datetime(2016, 10, 8, 17, 0, 0, tzinfo=to_zone)
Repository('path/to/the/repo', to=dt1).traverse_commits()

# !!!!! ERROR !!!!! THIS IS NOT POSSIBLE
Repository('path/to/the/repo', from_tag=from_tag, from_commit=from_commit).traverse_commits()

IMPORTANT: it is not possible to configure more than one filter of the same category (for example, more than one from). It is also not possible to have the single filter together with other filters!

Filtering commits

PyDriller comes with a set of common commit filters that you can apply:

  • only_in_branch (str): only analyses commits that belong to this branch.
  • only_no_merge (bool): only analyses commits that are not merge commits.
  • only_authors (List[str]): only analyses commits that are made by these authors. The check is made on the username, NOT the email.
  • only_commits (List[str]): only these commits will be analyzed.
  • only_releases (bool): only commits that are tagged (“release” is a term of GitHub, does not actually exist in Git)
  • filepath (str): only commits that modified this file will be analyzed.
  • only_modifications_with_file_types (List[str]): only analyses commits in which at least one modification was done in that file type, e.g., if you pass “.java”, it will visit only commits in which at least one Java file was modified; clearly, it will skip other commits (e.g., commits that did not modify Java files).

Examples:

# Only commits in branch1
Repository('path/to/the/repo', only_in_branch='branch1').traverse_commits()

# Only commits in branch1 and no merges
Repository('path/to/the/repo', only_in_branch='branch1', only_no_merge=True).traverse_commits()

# Only commits of author "ishepard" (yeah, that's me)
Repository('path/to/the/repo', only_authors=['ishepard']).traverse_commits()

# Only these 3 commits
Repository('path/to/the/repo', only_commits=['hash1', 'hash2', 'hash3']).traverse_commits()

# Only commit that modified "Matricula.javax"
Repository('path/to/the/repo', filepath='Matricula.javax').traverse_commits()

# Only commits that modified a java file
Repository('path/to/the/repo', only_modifications_with_file_types=['.java']).traverse_commits()

Other Configurations

Some git commands, such as git diff, can be customized by the user. In this section, we report some of the customization that can be used within pydriller.

  • histogram (bool): uses git diff --histogram instead of the normal git. See Git Diff Algorithms.
  • include_refs (bool): whether to include refs and HEAD in commit analysis (equivalent of adding the flag --all).
  • include_remotes (bool): whether to include remote commits in analysis (equivalent of adding the flag --remotes).
  • clone_repo_to (str): if the repository is a URL, Pydriller will clone it in this directory.

Git Diff Algorithms

Git offers four different algorithms in git diff:

  • Myers (default)
  • Minimal (improved Myers)
  • Patience (try to give contextual diff)
  • Histogram (kind of enhanced patience)

Differences between four diff algorithms

Based on the comparison between Myers and Histogram in a study by Nugroho, et al (2019), various diff algorithms in the git diff command produced unequal diff outputs. From the result of patches analysis, they found that Histogram is better than Myers to show the changes of code that can be expected to recover the changing operations. Thus, in this tool, we implement histogram diff algorithm to consider differences in source code.