Question

I’m new to Python, so maybe I’m asking for something very easy but I can’t think of the problem in a Python way.

I have a compressed string. The idea is, if a character gets repeated 4-15 times, I make this change:

'0000' ---> '0|4'

If more than 15 times, I use a slash and two digits to represent the amount (working with hexadecimal values):

'00...(16 times)..0' ---> '0/10'

So, accustomed to other languages, my approach is the following:

def uncompress(line):
    verticalBarIndex = line.index('|')
    while verticalBarIndex!=-1:
        repeatedChar = line[verticalBarIndex-1:verticalBarIndex]
        timesRepeated = int(line[verticalBarIndex+1:verticalBarIndex+2], 16)
        uncompressedChars = [repeatedChar]
        for i in range(timesRepeated):
            uncompressedChars.append(repeatedChar)
        uncompressedString = uncompressedChars.join()
        line = line[:verticalBarIndex-1] + uncompressedString + line[verticalBarIndex+2:]
        verticalBarIndex = line.index('|') #next one

    slashIndex = line.index('/')
    while slashIndex!=-1:
        repeatedChar = line[slashIndex-1:slashIndex]
        timesRepeated = int(line[slashIndex+1:verticalBarIndex+3], 16)
        uncompressedChars = [repeatedChar]
        for i in range(timesRepeated):
            uncompressedChars.append(repeatedChar)
        uncompressedString = uncompressedChars.join()
        line = line[:slashIndex-1] + uncompressedString + line[slashIndex+3:]
        slashIndex = line.index('/') #next one
    return line

Which I know it is wrong, since strings are inmutable in Python, and I am changing line contents all the time until no ‘|’ or ‘/’ are present.

I know UserString exists, but I guess there is an easier and more Pythonish way of doing it, which would be great to learn.

Any help?

Answer 1

The changes necessary to get your code running with the sample strings:

Change .index() to .find(). .index() raises an exception if the substring isn’t found, .find() returns -1.

Change uncompressedChars.join() to ''.join(uncompressedChars).

Change timesRepeated = int(line[slashIndex+1:verticalBarIndex+3], 16) to timesRepeated = int(line[slashIndex+1:slashIndex+3], 16)

Set uncompressedChars = [] to start with, instead of uncompressedChars = [repeatedChar].

This should get it working properly. There are a lot of places where the code an be tidied and otpimised, but this works.