Why there is a run time error in this python program?

Question

I have C++ background and very new to Python. I might be making a simple mistake.

def make_polish(s) :
    no_of_pluses = 0
    polish_str = []
    i = 0
    for index in range(len(s)):
        print s[index]
        if '+' == s[index]:
            no_of_pluses = no_of_pluses + 1
        if '*' == s[index]:
            polish_str[i] = s[index-1] """Index out of range error here."""
            i = i + 1 
            polish_str[i] = s[index+1]
            i = i + 1
            polish_str[i] = '*'
            i = i + 1

    return polish_str 

print make_polish("3*4")

Can you please reformat the code so it's copy-pasteable into a Python REPL. — Ahmed Fasih
– Ahmed Fasih, Commented Jun 8, 2015 at 4:23
Please edit your code so that it has more consistent indentation. Also, mixing tabs and spaces is a very bad idea in python — inspectorG4dget
– inspectorG4dget, Commented Jun 8, 2015 at 4:25
Please suggest a light weight Python editor for windows. I used notepad++ for it. — qqqqq
– qqqqq, Commented Jun 8, 2015 at 5:21

warvariuc · Accepted Answer · 2015-06-08 04:28:02Z

8

Your list polish_str is always empty. You need to do:

polish_str.append(s[index-1])

Instead of:

polish_str[i] = s[index-1] # """Index out of range error here."""
i = i + 1

When you create the list polish_str = [] it's not allocating space for it as it does in C/C++. It's a dynamic data structure.

answered Jun 8, 2015 at 4:28

warvariuc

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1 Comment

qqqqq Over a year ago

Thansk it worked. It seems it is a linked list and I have to do a hidden "new" of C++.

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