CODEWITHSUNDEEP
pythonparameters
winwin
winwin

Reputation: 1797

How to get parameter names from a parametrized string?

What I'd like is:

param_str = "I like $thing_I_like and dislike $thing_I_dislike. What does $person_I_like like?"
get_params(param_str)  # -> ("thing_I_like", "thing_I_dislike", "person_I_like")

I've looked through string.Template, it does only substitution.

Is there a standard library way to do this? Because in case of regex, there would have to be a check if $smt is actually a valid Python variable name and so on.

Upvotes: 0

Views: 127

Answers (1)

jonrsharpe
jonrsharpe

Reputation: 121987

string.Template, or one of its subclasses, stores the compiled regex that will be used to find identifiers to replace as the pattern class attribute. Therefore you can do:

>>> from string import Template
>>> s = "I like $thing_I_like and dislike $thing_I_dislike. What does $person_I_like like?"
>>> Template.pattern.findall(s)
[('', 'thing_I_like', '', ''), ('', 'thing_I_dislike', '', ''), ('', 'person_I_like', '', '')]

The groups in the result are:

  • escaped (e.g. $$ -> "$");
  • named (e.g. $identifier -> "identifier");
  • braced (e.g. ${noun}ification -> "noun"); or
  • invalid ("any other delimiter pattern (usually a single delimiter)", e.g. $ -> "").

For your purposes, therefore, you probably want:

>>> [
...     named or braced
...     for escaped, named, braced, invalid in Template.pattern.findall(s)
...     if named or braced
... ]
['thing_I_like', 'thing_I_dislike', 'person_I_like']

Upvotes: 3

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