[BUG] Strings with many environment variables cause a RecursionError

[jorisguex]

When expanding long strings with many environment variables, a RecursionError occurs.
See a minimal reproducible error here:

# This causes 'RecursionError: maximum recursion depth exceeded'
import expandvars
long_string = " ".join("$VAR" for _ in range(1000))
expandvars.expand(long_string)

Manually increasing the Python recursion limit can increase how many environment variables can be expanded:

# No exception
import expandvars
import sys
sys.setrecursionlimit(2000)
long_string = " ".join("$VAR" for _ in range(1000))
expandvars.expand(long_string)

It seems like internal expand() and expand_vars() functions call each other recursively, causing the issue.

[sayanarijit]

Thanks for reporting. A rewrite (using iterative approach) has been pending for some time. I'll start working on it.