Git objects

Contents

In the first place Git is a key-value storage system. The values stored are called objects, there are four types (commits, trees, blobs and tags), for each type pygit2 has a Python class:

# Get the last commit
>>> head = repo.head

# Show commits and trees
>>> commit
<pygit2.Commit object at 0x7f9d2f3000b0>
>>> commit.tree
<pygit2.Tree object at 0x7f9d2f3000f0>

These four classes (Commit, Tree, Blob and Tag) inherit from the Object base class, which provides shared behaviour. A Git object is identified by a unique object id, which is a binary byte string; this is often represented as an hexadecimal text string:

>>> commit.oid
b'x\xde\xb5W\x8d\x01<\xdb\xdf\x08o\xa1\xd1\xa3\xe7\xd9\x82\xe8\x88\x8f'
>>> commit.hex
'78deb5578d013cdbdf086fa1d1a3e7d982e8888f'

The API of pygit2 accepts both the raw object id and its hexadecimal representation, the difference is done based on its type (a byte or a text string).

Objects can not be modified once they have been created.

This is the common interface for all Git objects:

pygit2.Object

Commits

A commit is a snapshot of the working dir with meta informations like author, committer and others.

pygit2.Commit

Signatures

The author and committer attributes of commit objects are Signature objects:

>>> commit.author
<pygit2.Signature object at 0x7f75e9b1f5f8>

pygit2.Signature

Creating commits

Commits can be created by calling the create_commit method of the repository with the following parameters:

>>> author = Signature('Alice Author', 'alice@authors.tld')
>>> committer = Signature('Cecil Committer', 'cecil@committers.tld')
>>> tree = repo.TreeBuilder().write()
>>> repo.create_commit(
... 'refs/heads/master', # the name of the reference to update
... author, committer, 'one line commit message\n\ndetailed commit message',
... tree, # binary string representing the tree object ID
... [] # list of binary strings representing parents of the new commit
... )
'#\xe4<u\xfe\xd6\x17\xa0\xe6\xa2\x8b\xb6\xdc35$\xcf-\x8b~'

Trees

A tree is a sorted collection of tree entries. It is similar to a folder or directory in a file system. Each entry points to another tree or a blob. A tree can be iterated, and partially implements the sequence and mapping interfaces:

# Number of entries
>>> tree = commit.tree
>>> len(tree)
6

# Iteration
>>> for entry in tree:
...     print(entry.hex, entry.name)
...
7151ca7cd3e59f3eab19c485cfbf3cb30928d7fa .gitignore
c36f4cf1e38ec1bb9d9ad146ed572b89ecfc9f18 COPYING
32b30b90b062f66957d6790c3c155c289c34424e README.md
c87dae4094b3a6d10e08bc6c5ef1f55a7e448659 pygit2.c
85a67270a49ef16cdd3d328f06a3e4b459f09b27 setup.py
3d8985bbec338eb4d47c5b01b863ee89d044bd53 test

# Get an entry by name
>>> entry = tree['pygit2.c']
>>> entry
<pygit2.TreeEntry object at 0xcc10f0>

# Get the object the entry points to
>>> blob = repo[entry.oid]
>>> blob
<pygit2.Blob object at 0xcc12d0>

This is the interface of a tree entry:

TreeEntry.name        -- name of the tree entry
TreeEntry.oid         -- the id of the git object
TreeEntry.hex         -- hexadecimal representation of the oid
TreeEntry.filemode    -- the Unix file attributes
TreeEntry.to_object() -- returns the git object (equivalent to repo[entry.oid])

pygit2.Tree

pygit2.TreeEntry

Blobs

A blob is equivalent to a file in a file system.:

# create a blob out of memory
>>> oid  = repo.create_blob('foo bar')
>>> blob = repo[oid]

Blob.data -- the contents of the blob, a byte string

pygit2.Blob

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