Navigating through a string and updating the value of string while navigating

Question

I have got the following code in Python (in PyCharm Community Edition):

def defer_tags(sentence):

    for letter in sentence:
        print(letter)
        if letter == '<':
            end_tag = sentence.find('>')
            sentence = sentence[end_tag+1:]
            print(sentence)

defer_tags("<h1>Hello")

It produced the following output:

current letter =  <
new_sentence =  Hello
current letter =  h
current letter =  1
current letter =  >
current letter =  H
current letter =  e
current letter =  l
current letter =  l
current letter =  o

Why does loop (letter) navigate through the entire string (sentence) even though the value of sentence has changed inside the loop ?

I am printing out the value of sentence after the change but it is not getting reflected in the loop iterations.

Strings are immutable in python. You create a new string at each loop run, but the loop itself runs on the initial string. — spectras, Oct 15 '16 at 14:19
Thanks spectras. I guess I will have to make a new variable to store the value of mutated string. — Niranjan Vengallur, Oct 15 '16 at 14:24

score 0 · Answer 1 · answered Oct 16 '16 at 12:26

0

To be explicit, try using beautiful soup following way:

>>> from BeautifulSoup import BeautifulSoup
>>> soup = BeautifulSoup('<h1>Hello<h1>')
>>> soup.text
u'Hello'

answered Oct 16 '16 at 12:26

andromeda

1
3

Nf4r · Answer 2 · 2016-10-15T16:26:20.503

-1

Better way to catch phrases from tags is just simple to use re.

import re
def defer_tags(sentence):
    return re.findall(r'>(.+)<', sentence)

defer_tags('<h1>Hello<h1>')
> ['Hello']
defer_tags('<h1>Hello</h1><h2>Ahoy</h2>')
> ['Hello', 'Ahoy']

This will work if the tags are full. Ie <h2>Hello</h2> of <h1>Ahoy</h1> <h2>XX</h2> etc.

edited Oct 15 '16 at 16:26

answered Oct 15 '16 at 14:34

Nf4r

1,390
1
7
9

I am getting the following output for both the cases: – Niranjan Vengallur Oct 15 '16 at 15:14
['Hello
'] ['Hello
Ahoy
'] – Niranjan Vengallur Oct 15 '16 at 15:15
You don't parse HTML with regular expressions. [Ever.](http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags/1732454#1732454). And as a counter-example to your idea: `
Hello
` – spectras Oct 16 '16 at 00:02

Navigating through a string and updating the value of string while navigating

2 Answers2

'] ['Hello

Ahoy

Hello