Python: Can we Loop inside a string?

Question

Like for example I have a string of HTML Ordered List. Inside that ordered list, I want to write n number of lists. How can I accomplish the task of adding the lists to this string?

Here is the example code:

    html = """
    <ol>
      <li>
        <!--Something-->
      </li>
      ... <!--n lists-->
      {}                   #str().format()
      <li>
        <!--Something-->
      </li>
    </ol>
    """
    for li in html_lists: #where li is <li>...</li> and is inside the python list.
      html.format(li)

As far as I know, Strings are immutable and .format() will add <li> at {}. Hence this won't work for more than one <li>.

.format() will not add <li> at {} it will create a new string that has li in the place of {} — Yoriz
– Yoriz, Commented Aug 18, 2013 at 15:55

Andrew Clark · Accepted Answer · 2013-08-18 15:54:39Z

2

Like you said, strings are immutable so just having html.format(li) on a line by itself won't do anything, you need to do html = html.format(li) because the first version won't modify html in place, it will return a result.

As for using a loop with str.format(), you should be able to use the following assuming each element in html_lists is a string that contains a single <li> entry:

html = html.format('\n'.join(html_lists))

This works because '\n'.join(html_lists) will construct a single string from your list of strings, which can then be passed to html.format() to replace the single {} with the content from every element in html_lists. Note that you could also use ''.join(html_lists), the newline is just there to make it more readable when html is displayed.

answered Aug 18, 2013 at 15:54

Andrew Clark

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unutbu · Accepted Answer · 2013-08-18 16:27:44Z

0

You could use lxml to build HTML:

import lxml.html as LH
import lxml.builder as builder
html_lists = 'one two three'.split()
E = builder.E
html = (
    E.ol(
        *([E.li('something')]
          + [E.li(item) for item in html_lists]
          + [E.li('else')])
        )
    )

print(LH.tostring(html, pretty_print=True))

prints

<ol>
<li>something</li>
<li>one</li>
<li>two</li>
<li>three</li>
<li>else</li>
</ol>

answered Aug 18, 2013 at 16:27

unutbu

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martineau · Accepted Answer · 2013-08-18 17:33:51Z

0

Python is really good for processing text, so here's an example using it to do what you want:

import textwrap

def indent(amt, s):
    dent = amt * ' '
    return ''.join(map(lambda i: dent+i+'\n', s.split('\n')[:-1])).rstrip()

ordered_list_html = textwrap.dedent('''\
    <ol>
    {}
    </ol>
''')

# create some test data
html_lists = [textwrap.dedent('''\
    <li>
      list #{}
    </li>
    ''').format(n) for n in xrange(5)]

print ordered_list_html.format(indent(2, ''.join(html_lists)))

Output:

<ol>
  <li>
    list #0
  </li>
  <li>
    list #1
  </li>
  <li>
    list #2
  </li>
  <li>
    list #3
  </li>
  <li>
    list #4
  </li>
</ol>

answered Aug 18, 2013 at 17:33

martineau

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