import re
 
line = "Float: __, string: __"
values = ["float", "string"]
obj = lambda:None
obj.i = -1
 
def repl(m, count, values):
	count.i += 1
	return f'%{len(m.group(1))}{"." if values[count.i] == "float" else ""}{(len(m.group(2) or ".")-1) if values[count.i] == "float" else ""}{"f" if values[count.i] == "float" else "s"}'
 
newLine = re.sub(r'(_+)(\._+)?',
    lambda m: repl(m, obj, values),
    line)
 
print(newLine)      
##Float: %2.0f, string: %2s
 

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