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dvc.api.open()

Opens a tracked file.

def open(path: str,
         repo: str = None,
         rev: str = None,
         remote: str = None,
         mode: str = "r",
         encoding: str = None)

Usage:

import dvc.api

with dvc.api.open(
        'get-started/data.xml',
        repo='https://github.com/iterative/dataset-registry'
        ) as fd:
    # ... fd is a file descriptor that can be processed normally.

Description

Open a data or model file tracked in a DVC project and generate a corresponding file object. The file can be tracked by DVC (as an output) or by Git.

The exact type of file object depends on the mode used. For more details, please refer to Python's open() built-in, which is used under the hood.

dvc.api.open() may only be used as a context manager (using the with keyword, as shown in the examples).

This function makes a direct connection to the remote storage (except for Google Drive), so the file contents can be streamed. Your code can process the data buffer as it's streamed, which optimizes memory usage.

Use dvc.api.read() to load the complete file contents in a single function call โ€“ no context manager involved. Neither function utilizes disc space.

Parameters

  • path (required) - location and file name of the target to open, relative to the root of the project (repo).
  • repo - specifies the location of the DVC project. It can be a URL or a file system path. Both HTTP and SSH protocols are supported for online Git repos (e.g. [user@]server:project.git). Default: The current project is used (the current working directory tree is walked up to find it).
  • rev - Git commit (any revision such as a branch or tag name, or a commit hash). If repo is not a Git repo, this option is ignored. Default: HEAD.
  • remote - name of the DVC remote to look for the target data. Default: The default remote of repo is used if a remote argument is not given. For local projects, the cache is tied before the default remote.
  • mode - specifies the mode in which the file is opened. Defaults to "r" (read). Mirrors the namesake parameter in builtin open().
  • encoding - codec used to decode the file contents to a string. This should only be used in text mode. Defaults to "utf-8". Mirrors the namesake parameter in builtin open().

Exceptions

  • dvc.exceptions.FileMissingError - file in path is missing from repo.
  • dvc.exceptions.PathMissingError - path cannot be found in repo.
  • dvc.exceptions.NoRemoteError - no remote is found.

Example: Use data or models from a DVC repository

Any file tracked in a DVC project (and stored remotely) can be processed directly in your Python code with this API. For example, an XML file tracked in a public DVC repo on GitHub can be processed like this:

from xml.sax import parse
import dvc.api
from mymodule import mySAXHandler

with dvc.api.open(
        'get-started/data.xml',
        repo='https://github.com/iterative/dataset-registry'
        ) as fd:
    parse(fd, mySAXHandler)

Notice that we use a SAX XML parser here because dvc.api.open() is able to stream the data from remote storage. (The mySAXHandler object should handle the event-driven parsing of the document in this case.) This increases the performance of the code (minimizing memory usage), and is typically faster than loading the whole data into memory.

If you just needed to load the complete file contents into memory, you can use dvc.api.read() instead:

from xml.dom.minidom import parse
import dvc.api

xmldata = dvc.api.read('get-started/data.xml',
    repo='https://github.com/iterative/dataset-registry')
xmldom = parse(xmldata)

Example: Accessing private repos

This is just a matter of using the right repo argument, for example an SSH URL (requires that the credentials are configured locally):

import dvc.api

with dvc.api.open(
        'features.dat',
        repo='git@server.com:path/to/repo.git'
        ) as fd:
    # ... Process 'features'

Example: Use different versions of data

The rev argument lets you specify any Git commit to look for an artifact. This way any previous version, or alternative experiment can be accessed programmatically. For example, let's say your DVC repo has tagged releases of a CSV dataset:

import csv
import dvc.api

with dvc.api.open(
        'clean.csv',
        rev='v1.1.0'
        ) as fd:
    reader = csv.reader(fd)
    # ... Process 'clean' data from version 1.1.0

Also, notice that we didn't supply a repo argument in this example. DVC will attempt to find a DVC project to use in the current working directory tree, and look for the file contents of clean.csv in its local cache; no download will happen if found. See the Parameters section for more info.

Example: Choose a specific remote as the data source

Sometimes we may want to choose the remote data source, for example if the repo has no default remote set. This can be done by providing a remote argument:

import dvc.api

with dvc.api.open(
        'activity.log',
        repo='location/of/dvc/project',
        remote='my-s3-bucket'
        ) as fd:
    for line in fd:
        match = re.search(r'user=(\w+)', line)
        # ... Process users activity log

Example: Specify the text encoding

To chose which codec to open a text file with, send an encoding argument:

import dvc.api

with dvc.api.open(
        'data/nlp/words_ru.txt',
        encoding='koi8_r') as fd:
    # ... Process Russian words