DeepL Python Library

The DeepL API is a language translation API that allows other computer programs to send texts and documents to DeepL's servers and receive high-quality translations. This opens a whole universe of opportunities for developers: any translation product you can imagine can now be built on top of DeepL's best-in-class translation technology.

The DeepL Python library offers a convenient way for applications written in Python to interact with the DeepL API. We intend to support all API functions with the library, though support for new features may be added to the library after they’re added to the API.

Getting an authentication key

To use the DeepL Python Library, you'll need an API authentication key. To get a key, please create an account here. With a DeepL API Free account you can translate up to 500,000 characters/month for free.

Installation

The library can be installed from PyPI using pip:

pip install --upgrade deepl

If you need to modify this source code, install the dependencies using poetry:

poetry install

On Ubuntu 22.04 an error might occur: ModuleNotFoundError: No module named 'cachecontrol'. Use the workaround sudo apt install python3-cachecontrol as explained in this bug report.

Requirements

The library is tested with Python versions 3.6 to 3.10.

The requests module is used to perform HTTP requests; the minimum is version 2.0.

Usage

Import the package and construct a Translator. The first argument is a string containing your API authentication key as found in your DeepL Pro Account.

Be careful not to expose your key, for example when sharing source code.

import deepl

auth_key = "f63c02c5-f056-..."  # Replace with your key
translator = deepl.Translator(auth_key)

result = translator.translate_text("Hello, world!", target_lang="FR")
print(result.text)  # "Bonjour, le monde !"

This example is for demonstration purposes only. In production code, the authentication key should not be hard-coded, but instead fetched from a configuration file or environment variable.

Translator accepts additional options, see Configuration for more information.

Translating text

To translate text, call translate_text(). The first argument is a string containing the text you want to translate, or a list of strings if you want to translate multiple texts.

source_lang and target_lang specify the source and target language codes respectively. The source_lang is optional, if it is unspecified the source language will be auto-detected.

Language codes are case-insensitive strings according to ISO 639-1, for example 'DE', 'FR', 'JA''. Some target languages also include the regional variant according to ISO 3166-1, for example 'EN-US', or 'PT-BR'. The full list of supported languages is in the API documentation.

There are additional optional arguments to control translation, see Text translation options below.

translate_text() returns a TextResult, or a list of TextResults corresponding to your input text(s). TextResult has two properties: text is the translated text, and detected_source_lang is the detected source language code.

# Translate text into a target language, in this case, French:
result = translator.translate_text("Hello, world!", target_lang="FR")
print(result.text)  # "Bonjour, le monde !"

# Translate multiple texts into British English
result = translator.translate_text(
    ["お元気ですか？", "¿Cómo estás?"], target_lang="EN-GB"
)
print(result[0].text)  # "How are you?"
print(result[0].detected_source_lang)  # "JA" the language code for Japanese
print(result[1].text)  # "How are you?"
print(result[1].detected_source_lang)  # "ES" the language code for Spanish

# Translate into German with less and more Formality:
print(
    translator.translate_text(
        "How are you?", target_lang="DE", formality="less"
    )
)  # 'Wie geht es dir?'
print(
    translator.translate_text(
        "How are you?", target_lang="DE", formality="more"
    )
)  # 'Wie geht es Ihnen?'

Text translation options

In addition to the input text(s) argument, the available translate_text() arguments are:

• source_lang: Specifies the source language code, but may be omitted to auto-detect the source language.
• target_lang: Required. Specifies the target language code.
• split_sentences: specify how input text should be split into sentences, default: 'on'.
  • 'on'' (SplitSentences.ON): input text will be split into sentences using both newlines and punctuation.
  • 'off' (SplitSentences.OFF): input text will not be split into sentences. Use this for applications where each input text contains only one sentence.
  • 'nonewlines' (SplitSentences.NO_NEWLINES): input text will be split into sentences using punctuation but not newlines.
• preserve_formatting: controls automatic-formatting-correction. Set to True to prevent automatic-correction of formatting, default: False.
• formality: controls whether translations should lean toward informal or formal language. This option is only available for some target languages, see Listing available languages.
  • 'less' (Formality.LESS): use informal language.
  • 'more' (Formality.MORE): use formal, more polite language.
• glossary: specifies a glossary to use with translation, either as a string containing the glossary ID, or a GlossaryInfo as returned by get_glossary().
• tag_handling: type of tags to parse before translation, options are 'html' and 'xml'.

The following options are only used if tag_handling is 'xml':

• outline_detection: specify False to disable automatic tag detection, default is True.
• splitting_tags: list of XML tags that should be used to split text into sentences. Tags may be specified as an array of strings (['tag1', 'tag2']), or a comma-separated list of strings ('tag1,tag2'). The default is an empty list.
• non_splitting_tags: list of XML tags that should not be used to split text into sentences. Format and default are the same as for splitting_tags.
• ignore_tags: list of XML tags that containing content that should not be translated. Format and default are the same as for splitting_tags.

For a detailed explanation of the XML handling options, see the API documentation.

Translating documents

To translate documents, you may call either translate_document() using file IO objects, or translate_document_from_filepath() using file paths. For both functions, the first and second arguments correspond to the input and output files respectively.

Just as for the translate_text() function, the source_lang and target_lang arguments specify the source and target language codes.

There are additional optional arguments to control translation, see Document translation options below.

# Translate a formal document from English to German
input_path = "/path/to/Instruction Manual.docx"
output_path = "/path/to/Bedienungsanleitung.docx"
try:
    # Using translate_document_from_filepath() with file paths 
    translator.translate_document_from_filepath(
        input_path,
        output_path,
        target_lang="DE",
        formality="more"
    )

    # Alternatively you can use translate_document() with file IO objects
    with open(input_path, "rb") as in_file, open(output_path, "wb") as out_file:
        translator.translate_document(
            in_file,
            out_file,
            target_lang="DE",
            formality="more"
        )

except deepl.DocumentTranslationException as error:
    # If an error occurs during document translation after the document was
    # already uploaded, a DocumentTranslationException is raised. The
    # document_handle property contains the document handle that may be used to
    # later retrieve the document from the server, or contact DeepL support.
    doc_id = error.document_handle.id
    doc_key = error.document_handle.key
    print(f"Error after uploading ${error}, id: ${doc_id} key: ${doc_key}")
except deepl.DeepLException as error:
    # Errors during upload raise a DeepLException
    print(error)

translate_document() and translate_document_from_filepath() are convenience functions that wrap multiple API calls: uploading, polling status until the translation is complete, and downloading. If your application needs to execute these steps individually, you can instead use the following functions directly:

• translate_document_upload(),
• translate_document_get_status() (or translate_document_wait_until_done()), and
• translate_document_download()

Document translation options

In addition to the input file, output file, source_lang and target_lang arguments, the available translate_document() and translate_document_from_filepath() arguments are:

• formality: same as in Text translation options.
• glossary: same as in Text translation options.

Glossaries

Glossaries allow you to customize your translations using user-defined terms. Multiple glossaries can be stored with your account, each with a user-specified name and a uniquely-assigned ID.

Creating a glossary

You can create a glossary with your desired terms and name using create_glossary(). Each glossary applies to a single source-target language pair. Note: Glossaries are only supported for some language pairs, see Listing available glossary languages for more information. The entries should be specified as a dictionary.

If successful, the glossary is created and stored with your DeepL account, and a GlossaryInfo object is returned including the ID, name, languages and entry count.

# Create an English to German glossary with two terms:
entries = {"artist": "Maler", "prize": "Gewinn"}
my_glossary = translator.create_glossary(
    "My glossary",
    source_lang="EN",
    target_lang="DE",
    entries=entries,
)
print(
    f"Created '{my_glossary.name}' ({my_glossary.glossary_id}) "
    f"{my_glossary.source_lang}->{my_glossary.target_lang} "
    f"containing {my_glossary.entry_count} entries"
)
# Example: Created 'My glossary' (559192ed-8e23-...) EN->DE containing 2 entries

You can also upload a glossary downloaded from the DeepL website using create_glossary_from_csv(). Instead of supplying the entries as a dictionary, specify the CSV data as csv_data either as a file-like object or string or bytes containing file content:

# Open the CSV file assuming UTF-8 encoding. If your file contains a BOM,
# consider using encoding='utf-8-sig' instead.
with open('/path/to/glossary_file.csv', 'r',  encoding='utf-8') as csv_file:
    csv_data = csv_file.read()  # Read the file contents as a string
    my_csv_glossary = translator.create_glossary_from_csv(
        "CSV glossary",
        source_lang="EN",
        target_lang="DE",
        csv_data=csv_data,
    )

The API documentation explains the expected CSV format in detail.

Getting, listing and deleting stored glossaries

Functions to get, list, and delete stored glossaries are also provided:

• get_glossary() takes a glossary ID and returns a GlossaryInfo object for a stored glossary, or raises an exception if no such glossary is found.
• list_glossaries() returns a list of GlossaryInfo objects corresponding to all of your stored glossaries.
• delete_glossary() takes a glossary ID or GlossaryInfo object and deletes the stored glossary from the server, or raises an exception if no such glossary is found.

# Retrieve a stored glossary using the ID
glossary_id = "559192ed-8e23-..."
my_glossary = translator.get_glossary(glossary_id)

# Find and delete glossaries named 'Old glossary'
glossaries = translator.list_glossaries()
for glossary in glossaries:
    if glossary.name == "Old glossary":
        translator.delete_glossary(glossary)

Listing entries in a stored glossary

The GlossaryInfo object does not contain the glossary entries, but instead only the number of entries in the entry_count property.

To list the entries contained within a stored glossary, use get_glossary_entries() providing either the GlossaryInfo object or glossary ID:

entries = translator.get_glossary_entries(my_glossary)
print(entries)  # "{'artist': 'Maler', 'prize': 'Gewinn'}"

Using a stored glossary

You can use a stored glossary for text translation by setting the glossary argument to either the glossary ID or GlossaryInfo object. You must also specify the source_lang argument (it is required when using a glossary):

text = "The artist was awarded a prize."
with_glossary = translator.translate_text(
    text, source_lang="EN", target_lang="DE", glossary=my_glossary,
)
print(with_glossary)  # "Der Maler wurde mit einem Gewinn ausgezeichnet."

# For comparison, the result without a glossary:
without_glossary = translator.translate_text(text, target_lang="DE")
print(without_glossary)  # "Der Künstler wurde mit einem Preis ausgezeichnet."

Using a stored glossary for document translation is the same: set the glossary argument and specify the source_lang argument:

translator.translate_document(
    in_file, out_file, source_lang="EN", target_lang="DE", glossary=my_glossary,
)

The translate_document(), translate_document_from_filepath() and translate_document_upload() functions all support the glossary argument.

Checking account usage

To check account usage, use the get_usage() function.

The returned Usage object contains three usage subtypes: character, document and team_document. Depending on your account type, some usage subtypes may be invalid; this can be checked using the valid property. For API accounts:

• usage.character.valid is True,
• usage.document.valid and usage.team_document.valid are False.

Each usage subtype (if valid) has count and limit properties giving the amount used and maximum amount respectively, and the limit_reached property that checks if the usage has reached the limit. The top level Usage object has the any_limit_reached property to check all usage subtypes.

usage = translator.get_usage()
if usage.any_limit_reached:
    print('Translation limit reached.')
if usage.character.valid:
    print(
        f"Character usage: {usage.character.count} of {usage.character.limit}")
if usage.document.valid:
    print(f"Document usage: {usage.document.count} of {usage.document.limit}")

Listing available languages

You can request the list of languages supported by DeepL for text and documents using the get_source_languages() and get_target_languages() functions. They both return a list of Language objects.

The name property gives the name of the language in English, and the code property gives the language code. The supports_formality property only appears for target languages, and indicates whether the target language supports the optional formality parameter.

print("Source languages:")
for language in translator.get_source_languages():
    print(f"{language.name} ({language.code})")  # Example: "German (DE)"

print("Target languages:")
for language in translator.get_target_languages():
    if language.supports_formality:
        print(f"{language.name} ({language.code}) supports formality")
        # Example: "Italian (IT) supports formality"
    else:
        print(f"{language.name} ({language.code})")
        # Example: "Lithuanian (LT)"

Listing available glossary languages

Glossaries are supported for a subset of language pairs. To retrieve those languages use the get_glossary_languages() function, which returns an array of GlossaryLanguagePair objects. Each has source_lang and target_lang properties indicating that that pair of language codes is supported.

glossary_languages = translator.get_glossary_languages()
for language_pair in glossary_languages:
    print(f"{language_pair.source_lang} to {language_pair.target_lang}")
    # Example: "EN to DE", "DE to EN", etc.

You can also find the list of supported glossary language pairs in the API documentation.

Note that glossaries work for all target regional-variants: a glossary for the target language English ("EN") supports translations to both American English ("EN-US") and British English ("EN-GB").

Exceptions

All module functions may raise deepl.DeepLException or one of its subclasses. If invalid arguments are provided, they may raise the standard exceptions ValueError and TypeError.

Configuration

Logging

Logging can be enabled to see the HTTP requests sent and responses received by the library. Enable and control logging using Python's logging module, for example:

import logging

logging.basicConfig()
logging.getLogger('deepl').setLevel(logging.DEBUG)

Server URL configuration

You can override the URL of the DeepL API by specifying the server_url argument when constructing a deepl.Translator. This may be useful for testing purposes. You do not need to specify the URL to distinguish API Free and API Pro accounts, the library selects the correct URL automatically.

server_url = "http://user:pass@localhost:3000"
translator = deepl.Translator(..., server_url=server_url)

Proxy configuration

You can configure a proxy by specifying the proxy argument when constructing a deepl.Translator:

proxy = "http://user:[email protected]:3128"
translator = deepl.Translator(..., proxy=proxy)

The proxy argument is passed to the underlying requests session, see the documentation for requests; a dictionary of schemes to proxy URLs is also accepted.

Command Line Interface

The library can be run on the command line supporting all API functions. Use the --help option for usage information:

python3 -m deepl --help

The CLI requires your DeepL authentication key specified either as the DEEPL_AUTH_KEY environment variable, or using the --auth-key option, for example:

python3 -m deepl --auth-key=YOUR_AUTH_KEY usage

Note that the --auth-key argument must appear before the command argument. The recognized commands are:

Command	Description
text	translate text(s)
document	translate document(s)
usage	print usage information for the current billing period
languages	print available languages
glossary	create, list, and remove glossaries

For example, to translate text:

python3 -m deepl --auth-key=YOUR_AUTH_KEY text --to=DE "Text to be translated."

Wrap text arguments in quotes to prevent the shell from splitting sentences into words.

Issues

If you experience problems using the library, or would like to request a new feature, please open an issue.

Development

We welcome Pull Requests, please read the contributing guidelines.

Tests

Execute the tests using pytest. The tests communicate with the DeepL API using the auth key defined by the DEEPL_AUTH_KEY environment variable.

Be aware that the tests make DeepL API requests that contribute toward your API usage.

The test suite may instead be configured to communicate with the mock-server provided by deepl-mock. Although most test cases work for either, some test cases work only with the DeepL API or the mock-server and will be otherwise skipped. The test cases that require the mock-server trigger server errors and test the client error-handling. To execute the tests using deepl-mock, run it in another terminal while executing the tests. Execute the tests using pytest with the DEEPL_MOCK_SERVER_PORT and DEEPL_SERVER_URL environment variables defined referring to the mock-server.