How do I find the name of the conda environment in which my code is running?

Edit: Oops, I hadn't noticed Ivo's answer. Let's say that I am expanding a little bit on it.

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If you run your python script from terminal:

import os
os.system("conda env list")

This will list all conda environments, as from terminal with conda env list.

Slightly better:

import os
_ = os.system("conda env list | grep '*'")

The _ = bit will silence the exist status of the call to os.system (0 if successful), and grep will only print out the line with the activated conda environment.

If you don't run your script from terminal (e.g. it is scheduled via crontab), then the above won't have anywhere to "print" the result. Instead, you need to use something like python's subprocess module. The simplest solution is probably to run:

import subprocess
output = subprocess.check_output("conda env list | grep '*'", shell=True, encoding='utf-8')
print(output)

Namely output is a string containing the output of the command conda env list, not its exit status (that too can be retrieved, see documentation of the subprocess module).

Now that you have a string with the information on the activated conda environment, you can perform whichever test you need (using regular expressions) to perform (or not) the installs mentioned in your question.

Remark.
Of course, print(output) in the block above will have no effect if your script is not run from terminal, but if you test the block in a script which you run from terminal, then you can verify that it gives you what you want. You can for instance print this information into a log file (using the logging module is recommended).

You want $CONDA_DEFAULT_ENV or $CONDA_PREFIX:

$ source activate my_env
(my_env) $ echo $CONDA_DEFAULT_ENV
my_env

(my_env) $ echo $CONDA_PREFIX
/Users/nhdaly/miniconda3/envs/my_env

$ source deactivate
$ echo $CONDA_DEFAULT_ENV  # (not-defined)

$ echo $CONDA_PREFIX  # (not-defined)

In python:

import os
print(os.environ['CONDA_DEFAULT_ENV'])

for the absolute entire path which is usually more useful:

Python 3.9.0 | packaged by conda-forge | (default, Oct 14 2020, 22:56:29) 
[Clang 10.0.1 ] on darwin
import os; print(os.environ["CONDA_PREFIX"])
/Users/miranda9/.conda/envs/synthesis

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The environment variables are not well documented. You can find CONDA_DEFAULT_ENV mentioned here: https://www.continuum.io/blog/developer/advanced-features-conda-part-1

The only info on CONDA_PREFIX I could find is this Issue: https://github.com/conda/conda/issues/2764

conda info

directly lists all the information where in the first lines you can see the

active environment: (some name)
active env location: (location of active environment)

I guess this is the most clear way.

In an interactive environment like Jupyter Notebook or Jupyter Lab, you should use % before typing the commands, like the following,

%conda info

I am using this:

import sys
sys.executable.split('/')[-3]

it has the advantage that it doesn't assume the env is in the path (and is nested under envs). Also, it does not require the environment to be activated via source activate.

Edit: If you want to make sure it works on Windows, too:

import sys
from pathlib import Path
Path(sys.executable).as_posix().split('/')[-3]

To clarify: sys.executable gives you the path of the current python interpreter (regardless of activate/deactivate) -- for instance '/Users/danielsc/miniconda3/envs/nlp/bin/python'. The rest of the code just takes the 3rd from last path segment, which is the name of the folder the environment is in, which is usually also the name of the python environment.