Python – How to update an existing Conda environment with a .yml file

anacondacondadjangopython

How can a pre-existing conda environment be updated with another .yml file. This is extremely helpful when working on projects that have multiple requirement files, i.e. base.yml, local.yml, production.yml, etc.

For example, below is a base.yml file has conda-forge, conda, and pip packages:

base.yml

name: myenv
channels:
  - conda-forge
dependencies:
  - django=1.10.5
  - pip:
    - django-crispy-forms==1.6.1

The actual environment is created with:
conda env create -f base.yml.

Later on, additional packages need to be added to base.yml. Another file, say local.yml, needs to import those updates.

Previous attempts to accomplish this include:

creating a local.yml file with an import definition:

channels:

dependencies:
  - pip:
    - boto3==1.4.4
imports:
  - requirements/base.

And then run the command:
conda install -f local.yml.

This does not work. Any thoughts?

Best Answer

Try using conda env update:

conda activate myenv
conda env update --file local.yml --prune

--prune uninstalls dependencies which were removed from local.yml, as pointed out in this answer by @Blink.

Or without the need to activate the environment (thanks @NumesSanguis):

conda env update --name myenv --file local.yml --prune

See Updating an environment in Conda User Guide.

Related Solutions

Python – How to check whether a file exists without exceptions

If the reason you're checking is so you can do something like if file_exists: open_it(), it's safer to use a try around the attempt to open it. Checking and then opening risks the file being deleted or moved or something between when you check and when you try to open it.

If you're not planning to open the file immediately, you can use os.path.isfile

Return True if path is an existing regular file. This follows symbolic links, so both islink() and isfile() can be true for the same path.

import os.path
os.path.isfile(fname)

if you need to be sure it's a file.

Starting with Python 3.4, the pathlib module offers an object-oriented approach (backported to pathlib2 in Python 2.7):

from pathlib import Path

my_file = Path("/path/to/file")
if my_file.is_file():
    # file exists

To check a directory, do:

if my_file.is_dir():
    # directory exists

To check whether a Path object exists independently of whether is it a file or directory, use exists():

if my_file.exists():
    # path exists

You can also use resolve(strict=True) in a try block:

try:
    my_abs_path = my_file.resolve(strict=True)
except FileNotFoundError:
    # doesn't exist
else:
    # exists

Python – How to copy a file in Python

shutil has many methods you can use. One of which is:

from shutil import copyfile
copyfile(src, dst)

# 2nd option
copy(src, dst)  # dst can be a folder; use copy2() to preserve timestamp

Copy the contents of the file named src to a file named dst. Both src and dst need to be the entire filename of the files, including path.
The destination location must be writable; otherwise, an IOError exception will be raised.
If dst already exists, it will be replaced.
Special files such as character or block devices and pipes cannot be copied with this function.
With copy, src and dst are path names given as strs.

Another shutil method to look at is shutil.copy2(). It's similar but preserves more metadata (e.g. time stamps).

If you use os.path operations, use copy rather than copyfile. copyfile will only accept strings.

Best Answer

Related Solutions

Python – How to check whether a file exists without exceptions

Python – How to copy a file in Python

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