I have the following sample string:

 R10666: 273141 C1 + 273141 C2 + 273141 C3 + 273141 C4 + 273141 C5 - 273141 C6

I want to obtain:

[('273141','C1'), ..., ('- 273141', 'C6')]

The numbers can be floating point numbers with exponential notation i.e. - 2.5e-7.

My current regex looks like this:

re.findall(r'([+-]? \d+(\.\d*)?|\.\d+([eE][+-]?\d+)?)( [a-zA-Z0-9_]+)', split)

But it doesn't produce the correct output, what is wrong with it?

This is a sample output:

(' 273141', '', '', ' C1')

or it matches nothing.

findall will put all the submatches in the results. In your case, the empty strings come from the unmatched decimals if they are present; so use non-capture groups instead:

([+-]? \d+(?:\.\d*)?|\.\d+(?:[eE][+-]?\d+)?) ([a-zA-Z0-9_]+)

I also moved the space at the second capture group outside so you don't get that leading space.

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