There are four types of Git objects: blobs, trees, commits and tags. For each one pygit2 has a type, and all four types inherit from the base Object type.
Contents
In the previous chapter we learnt about Object IDs. With an oid we can ask the repository to get the associated object. To do that the Repository class implementes a subset of the mapping interface.
The Object type is a base type, it is not possible to make instances of it, in any way.
It is the base type of the Blob, Tree, Commit and Tag types, so it is possible to check whether a Python value is an Object or not:
>>> from pygit2 import Object
>>> commit = repository.revparse_single('HEAD')
>>> print isinstance(commit, Object)
True
All Objects are immutable, they cannot be modified once they are created:
>>> commit.message = u"foobar"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: attribute 'message' of '_pygit2.Commit' objects is not writable
Derived types (blobs, trees, etc.) don’t have a constructor, this means they cannot be created with the common idiom:
>>> from pygit2 import Blob
>>> blob = Blob("data")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot create '_pygit2.Blob' instances
New objects are created using an specific API we will see later.
This is the common interface for all Git objects:
A blob is just a raw byte string. They are the Git equivalent to files in a filesytem.
This is their API:
There are a number of methods in the repository to create new blobs, and add them to the Git object database:
There are also some functions to calculate the oid for a byte string without creating the blob object:
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.
Example:
>>> tree = commit.tree
>>> len(tree) # Number of entries
6
>>> for entry in tree: # Iteration
... print(entry.id, entry.name)
...
7151ca7cd3e59f3eab19c485cfbf3cb30928d7fa .gitignore
c36f4cf1e38ec1bb9d9ad146ed572b89ecfc9f18 COPYING
32b30b90b062f66957d6790c3c155c289c34424e README.md
c87dae4094b3a6d10e08bc6c5ef1f55a7e448659 pygit2.c
85a67270a49ef16cdd3d328f06a3e4b459f09b27 setup.py
3d8985bbec338eb4d47c5b01b863ee89d044bd53 test
>>> entry = tree['pygit2.c'] # Get an entry by name
>>> entry
<pygit2.TreeEntry object at 0xcc10f0>
>>> blob = repo[entry.id] # Get the object the entry points to
>>> blob
<pygit2.Blob object at 0xcc12d0>
A commit is a snapshot of the working dir with meta informations like author, committer and others.
The author and committer attributes of commit objects are Signature objects:
>>> commit.author
<pygit2.Signature object at 0x7f75e9b1f5f8>
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~'