Pythonic way to append list of strings to an array

Question

I'm new to Python and come from a Java background. I'd like to know the most Pythonic way of writing this code:

entry_list = []
for entry in feed.entry:
    entry_list.append(entry.title.text)

Basically for each element in the feed, I'd like to append that element's title to a list.

I don't know if I should use a map() or lambda function or what...

Thanks

@pst that's no help at all. i know how to write the code multiple ways, i'm asking for other people's advice for the best way to do it. — Cuga
– Cuga, Commented Nov 5, 2011 at 15:27
I could swear it covers all the methods below -- list comprehensions in particular ;-) — user166390
– user166390, Commented Nov 5, 2011 at 18:05
Right, it has a multitude of ways to approach the problem, including the one I took... I need advice for which one to choose. — Cuga
– Cuga, Commented Nov 7, 2011 at 19:16

Serdalis · Accepted Answer · 2011-11-03 04:55:17Z

8

most pythonic code I can think of:

entry_list = [entry.title.text for entry in feed.entry]

This is a list comprehension which will construct a new list out of the elements in feed.entry.title.text.

To append you will need to do:

entry_list.extend([entry.title.text for entry in feed.entry])

As a side note, when doing extend operations, the normally fast generator expression is much slower than a list comprehension.

edited Nov 3, 2011 at 4:55

answered Nov 3, 2011 at 4:25

Serdalis

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1 Comment

Ignacio Vazquez-Abrams Over a year ago

List comprehension. The list constructor is list().

Ignacio Vazquez-Abrams · Accepted Answer · 2011-11-03 04:24:55Z

4

With a little bit of trickery courtesy of a genex.

entry_list.extend(x.title.text for x in feed.entry)

Or just a LC if you don't need to keep the same list.

entry_list = [x.title.text for x in feed.entry]

answered Nov 3, 2011 at 4:24

Ignacio Vazquez-Abrams

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3 Comments

Serdalis Over a year ago

for some reason, list comprehensions are faster than generator sequences for the extend functionality.

Ignacio Vazquez-Abrams Over a year ago

Makes sense. With a LC it can just reallocate the list all in one go, whereas with a genex it has to reallocate for each yielded value or so.

Cuga Over a year ago

Thanks, I forgot about list comprehension

Abdul Muneer · Accepted Answer · 2011-11-03 04:37:52Z

3

Always use List Comprehension for concise expressions.

entry_list = [entry.title.text for entry in feed.entry]

If all that you want to do with the entry_list is to iterate over it again, you can use the generator expression

entry_list = (entry.title.text for entry in feed.entry)

Notice that the only difference is in using parenthesis. When using the generator format, the entry_list is not populated and can save the memory. You will still be able to do things like

for items in entry_list:
    do something

and

''.join(entry_list)

answered Nov 3, 2011 at 4:37

Abdul Muneer

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