chembl_downloader
Don't worry about downloading/extracting ChEMBL or versioning - just use chembl_downloader to write code that knows how to download it and use it automatically.
Installation
$ pip install chembl-downloader
Usage
Download A Specific Version
import chembl_downloader
path = chembl_downloader.download(version='28')
After it's been downloaded and extracted once, it's smart and does not need to download again. It gets stored
using pystow automatically in the ~/.data/chembl
directory.
We'd like to implement something such that it could load directly into SQLite from the archive, but it appears this is
a paid feature.
Download the Latest Version
First, you'll have to install bioversions
with pip install bioversions, whose job it is to look up the latest version of many databases. Then, you can modify
the previous code slightly by omitting the version keyword argument:
import chembl_downloader
path = chembl_downloader.download()
The version keyword argument is available for all functions in this package (e.g., including
connect(), cursor(), and query()), but will be omitted below for brevity.
Automate Connection
Inside the archive is a single SQLite database file. Normally, people manually untar this folder then
do something with the resulting file. Don't do this, it's not reproducible!
Instead, the file can be downloaded and a connection can be opened automatically with:
import chembl_downloader
with chembl_downloader.connect() as conn:
with conn.cursor() as cursor:
cursor.execute(...) # run your query string
rows = cursor.fetchall() # get your results
The cursor() function provides a convenient wrapper around this operation:
import chembl_downloader
with chembl_downloader.cursor() as cursor:
cursor.execute(...) # run your query string
rows = cursor.fetchall() # get your results
Run a query and get a pandas DataFrame
The most powerful function is query() which builds on the previous connect() function
in combination with pandas.read_sql
to make a query and load the results into a pandas DataFrame for any downstream use.
import chembl_downloader
sql = """
SELECT
MOLECULE_DICTIONARY.chembl_id,
MOLECULE_DICTIONARY.pref_name
FROM MOLECULE_DICTIONARY
JOIN COMPOUND_STRUCTURES ON MOLECULE_DICTIONARY.molregno == COMPOUND_STRUCTURES.molregno
WHERE molecule_dictionary.pref_name IS NOT NULL
LIMIT 5
"""
df = chembl_downloader.query(sql)
df.to_csv(..., sep='\t', index=False)
Suggestion 1: use pystow to make a reproducible file path that's portable to other people's machines
(e.g., it doesn't have your username in the path).
Suggestion 2: RDKit is now pip-installable with pip install rdkit-pypi, which means most users don't have
to muck around with complicated conda environments and configurations. One of the powerful but understated
tools in RDKit is the rdkit.Chem.PandasTools
module.
Store in a Different Place
If you want to store the data elsewhere using pystow (e.g., in pyobo
I also keep a copy of this file), you can use the prefix argument.
import chembl_downloader
# It gets downloaded/extracted to
# ~/.data/pyobo/raw/chembl/29/chembl_29/chembl_29_sqlite/chembl_29.db
path = chembl_downloader.download(prefix=['pyobo', 'raw', 'chembl'])
See the pystow documentation on configuring the storage
location further.
The prefix keyword argument is available for all functions in this package (e.g., including
connect(), cursor(), and query()).
Download via CLI
After installing, run the following CLI command to ensure it and send the path to stdout
$ chembl_downloader
Use --test to show two example queries
$ chembl_downloader --test
