More Commits via the GitHub API

I wrote a bit ago about making commits via the GitHub API. That post outlined making changes in two simplified situations: making changes to a single file and making updates to two existing files at the root of the repository. Here I show a more general solution that allows arbitrary changes anywhere in the repo.

I want to be able to specify a repo and branch and say "here are the contents of files that have changed or been created and here are the names of files that have been deleted, please take all that and this message and make a new commit for me." Because the GitHub API is so rudimentary when it comes to making commits that will end up being a many-stepped process, but it’s mostly the same steps repeated many times so it’s not a nightmare to code up. At a high level the process goes like this:

  • Get the current repo state from GitHub
    • This is the names and hashes of all the files and directories, but not the actual file contents.
  • Construct a local, malleable representation of the repo
  • Modify the local representation according to the given updates, creations, and deletions
  • Walk though the modified local "repo" and upload new/changed files and directories to GitHub
    • This must be done from the bottom up because a change at the low level means every directory above that level will need to be changed.
  • Make a new commit pointed at the new root tree (I’ll explain trees soon.)
  • Update the working branch to point to the new commit

This blob post is readable as an IPython Notebook at I’ve also reproduced the notebook below.

I’ll start off with the preliminaries that allow me to pull down the current repo state. I use the library for abstracting the GitHub API requests.

import os.path
from github3 import login

Basic information required for connecting to GitHub and which repo and branch to work on:

username = 'jiffyclub'
token = 'zzz'
repo_name = 'demodemo'
branch_name = 'master'

A Repository instance will be the main interface to the repo.

gh = login(username=username, token=token)
repo = gh.repository(username, repo_name)

To actually see repo contents we have to pick a specific branch. "Recursing" on the tree is how I get one long list of all the things in the repo.

# get the current repo layout
branch = repo.branch(branch_name)
tree = branch.commit.commit.tree.recurse()

The repository file structure is represented by a Tree object and individual things within the repo are represented by Hash objects.

h = tree.tree[0]
h.path, h.mode, h.sha, h.type

('', '100644', 'c385d5f2330a39aca84f2f7999346244bbf0a997', 'blob')

By looping over the tree I can print out the whole repo structure:

for h in tree.tree:

Malleable Local Repo

Git tracks repository state using two kinds of objects: blobs, which contain file contents, and trees, which contain file and directory names pointing to blobs and other trees.

My plan is to represent the current repository state locally, modify that local state, and finally add the changes to GitHub via the API.

def split_one(path):
    Utility function for splitting off the very first part of a path.
    path : str
    head, tail : str
    >>> split_one('a/b/c')
    ('a', 'b/c')
    >>> split_one('d')
    ('', 'd')
    s = path.split('/', 1)
    if len(s) == 1:
        return '', s[0]
        return tuple(s)


('dir1', 'dir2/dir3')

To match Git’s blobs and trees the core of my code will be two classes: File and Directory. File will be quite simple; it will know how to post a new blob to GitHub and not much else:

class File(object):
    Represents a file/blob in the repo.
    name : str
        Name of this file. Should contain no path components.
    mode : str
        '100644' for regular files, 
        '100755' for executable files.
    sha : str
        Git sha for an existing file, 
        omitted or None for a new/changed file.
    content : str
        File's contents as text. 
        Omitted or None for an existing file,
        must be given for a changed or new file.
    def __init__(self, name, mode, sha=None, content=None): = name
        self.mode = mode
        self.sha = sha
        self.content = content
    def create_blob(self, repo):
        Post this file to GitHub as a new blob.
        If this file is unchanged nothing will be done.
        repo : github3.repos.repo.Repository
            Authorized repository instance.
            Dictionary of info about the blob:
            path: blob's name
            type: 'blob'
            mode: blob's mode
            sha: blob's up-to-date sha
            changed: True if a new blob was created
        if self.sha:
            # already up to date
            print('Blob unchanged for {}'.format(
            changed = False
            assert self.content is not None
            print('Making blob for {}'.format(
            self.sha = repo.create_blob(self.content, encoding='utf-8')
            changed = True
        return {'path':,
                'type': 'blob',
                'mode': self.mode,
                'sha': self.sha,
                'changed': changed}

The Directory, with its listing of files and other directories, ties everything together. With the root directory we can find anything else in the repo. In fact, the hash of the root tree of a repo is what Git keeps a record of when you make a commit. Everything else is referenced off that tree and any trees it contains.

class Directory(object):
    Represents a directory/tree in the repo.
    name : str
        Name of directory. Should not contain any path components.
    sha : str
        Hash for an existing tree, omitted or None for a new tree.
    def __init__(self, name, sha=None): = name
        self.sha = sha
        self.files = {}
        self.directories = {}
        self.changed = False
    def add_directory(self, name, sha=None):
        Add a new subdirectory or return an existing one.
        name : str
            If this contains any path components new directories
            will be made to a depth necessary to construct the full path.
        sha : str
            Hash for an existing directory, omitted or None for a new directory.
            Reference to the named directory.
            If `name` contained multiple path components only the
            reference to the last directory referenced is returned.
        head, tail = split_one(name)
        if head and head not in self.directories:
            self.directories[head] = Directory(head)
        elif not head:
            # the input directory is a child of the current directory
            if name not in self.directories:
                self.directories[name] = Directory(name, sha)
            return self.directories[name]
        return self.directories[head].add_directory(tail, sha)
    def add_file(self, name, mode, sha=None, content=None):
        Add a new file. An existing file with the same name
        will be replaced.
        name : str
            Name of file. If it contains path components new
            directories will be made as necessary until the
            file can be made in the appropriate location.
        mode : str
            '100644' for regular files, 
            '100755' for executable files.
        sha : str
            Git hash for file. Required for existing files,
            omitted or None for new files.
        content : str
            Content of a new or changed file. Omit for existing files.
        head, tail = os.path.split(name)
        if not head:
            # this file belongs in this directory
            if mode is None:
                if tail in self.files:
                    # we're getting an update to an existing file
                    assert content is not None
                    mode = self.files[tail].mode
                    assert mode
                    raise ValueError('Adding a new file with no mode.')
            self.files[tail] = File(name, mode, sha, content)
            self.add_directory(head).add_file(tail, mode, sha, content)
    def delete_file(self, name):
        Delete a named file.
        name : str
            Name of file to delete. May contain path components.
        head, tail = os.path.split(name)
        if not head:
            # should be in this directory
            del self.files[tail]
            self.changed = True
    def create_tree(self, repo):
        Post a new tree to GitHub.
        If this directory and everything in/below it 
        are unchanged nothing will be done.
        repo : github3.repos.repo.Repository
            Authorized repository instance.
        tree_info : dict
            'path': directory's name
            'mode': '040000'
            'sha': directory's up-to-date hash
            'type': 'tree'
            'changed': True if a new tree was posted to GitHub
        tree = [f.create_blob(repo) for f in self.files.values()]
        tree = tree + [d.create_tree(repo) for d in self.directories.values()]
        tree = list(filter(None, tree))

        if not tree:
            # nothing left in this directory, it should be discarded
            return None

        # have any subdirectories or files changed (or been deleted)?
        changed = any(t['changed'] for t in tree) or self.changed
        if changed:
            print('Creating tree for {}'.format(
            tree = [{k: v for k, v in t.items() if k != 'changed'} for t in tree]
            self.sha = repo.create_tree(tree).sha
            print('Tree unchanged for {}'.format(
        assert self.sha
        return {'path':,
                'mode': '040000',
                'sha': self.sha,
                'type': 'tree',
                'changed': changed}

With the File and Directory classes defined I can construct the current repo state. Everything starts with the unnamed root directory. I filter out the blobs and trees so I can add the directories first, though this isn’t strictly necessary.

trees = [h for h in tree.tree if h.type == 'tree']
blobs = [h for h in tree.tree if h.type == 'blob']

root = Directory('', branch.commit.commit.tree.sha)

for h in trees:
    root.add_directory(h.path, h.sha)

for h in blobs:
    root.add_file(h.path, h.mode, h.sha)

Set up some changes and deletions

With the repo state reconstructed locally I’ll configure some changes. There are changes to existing files, new files, and file deletions.

# 'mode': None indicates it's an existing file and the mode should be kept as is
# New files must give a valid 'mode' parameter
updates = [{'path': '', 
            'content': 'a', 
            'mode': None},
           {'path': 'dir1/dir1-1.txt', 
            'content': 'b', 
            'mode': None},
           {'path': 'dir1/dir2/dir3/dir3-2.txt', 
            'content': 'c', 
            'mode': None},
           {'path': 'dir1/dir2/dir3/dir3-3.txt', 
            'content': 'e', 
            'mode': '100644'},
           {'path': 'root3.txt', 
            'content': 'f', 
            'mode': '100644'},
           {'path': 'dir6/dir7/dir7-1.txt', 
            'content': 'g', 
            'mode': '100644'}]

# paths to deleted files
deleted = ['root1.txt',

The next step is to update the local repo representation:

# make our local repo reflect how we want it to look
# after changing/adding/deleting files
for thing in updates:
    root.add_file(thing['path'], thing['mode'], content=thing['content'])

for d in deleted:

Make all the new blobs and trees created by the changes

The local repo representation now has the same structure I want the repo on GitHub to have. To get all the updates sent to GitHub I call the .create_tree method on the root directory. That method in turn calls the .create_tree and .create_blob methods on all the directories and files below, which in turn do the same. One by one each changed file and directory will have its data sent to GitHub and finally I’ll have the hash of the new root tree that I can use in a commit.

root_info = root.create_tree(repo)

Making blob for root3.txt
Blob unchanged for root2.txt
Making blob for
Blob unchanged for
Blob unchanged for dir1-2.txt
Making blob for dir1-1.txt
Blob unchanged for dir3-1.txt
Making blob for dir3-3.txt
Making blob for dir3-2.txt
Creating tree for dir3
Creating tree for dir2
Creating tree for dir1
Making blob for dir7-1.txt
Creating tree for dir7
Creating tree for dir6
Blob unchanged for dir8-2.txt
Creating tree for dir8
Blob unchanged for dir5-1.txt
Blob unchanged for dir5-2.txt
Tree unchanged for dir5
Creating tree for 


{'sha': '3f1e781ebde83629df62de0a869169d29c10e435',
 'path': '',
 'type': 'tree',
 'mode': '040000',
 'changed': True}

Make a new commit

At this point GitHub has all of my new data but there’s nothing in the history of my repo pointing at this new state. That requires making a new commit. The ingredients for a new commit are a message, the sha hash of a tree (from which can be derived the entire repo state), and a parent commit(s) for linking the new commit to the rest of the project history.

new_commit = repo.create_commit('Making a whole bunch of changes all over via the GitHub API.',


<Commit [Matt Davis:753e75b9891afac88ecc9fae86ec0bc11fa009c6]>



Update master branch to point to new commit

The commit is now part of my project’s history, but my working branch has not been updated to point at the new commit. This happens implicitly when you work with Git at the command line, but when working via the API it has to be done manually.

The procedure for this is to get a Reference instance for the working branch and use its .update method to point it at the new commit.

ref = repo.ref('heads/{}'.format(branch_name))


A return value of True indicates success.

What’s Missing

I haven’t made any attempt here to test symlinks or binary content like images. Those could require some special handling, but I think it’ll be maneagable.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s