alter / modify a list as well as iterate on its items / objects

[Derek Basch]

Hello,

Can anyone point me towards an article or explain
how to properly alter a list as well as iterate
on its items? For example:

input:

word = ["albert", "likes", "surfing!"]

for word in sentence:
word += "foo"

result:

word = ["albertfoo", "likesfoo", "surfingfoo"]

Thanks,
Derek Basch



__________________________________
Do you Yahoo!?
Friends. Fun. Try the all-new Yahoo! Messenger.
http://messenger.yahoo.com/

[Ryan Paul]

On Tue, 25 May 2004 12:57:32 -0700, Derek Basch wrote:

Hello,

Can anyone point me towards an article or explain
how to properly alter a list as well as iterate
on its items? For example:

input:

word = ["albert", "likes", "surfing!"]

for word in sentence:
word += "foo"

result:

word = ["albertfoo", "likesfoo", "surfingfoo"]

word = ["albert","likes","surfing!"]

you could do it with a map:

word = map(lambda x: x + "foo", words)

or with a list comprehension:

word = [x + "foo" for x in words]

[Larry Bates]

Most of the time this is done without
a loop at all as follows:

word = ["albert", "likes", "surfing!"]

word = [x+"foo" for x in word]

word = [""albertfoo", "likesfoo", "surfing!foo"]

Much of what you use loops for in other
languages you don't need in Python. List
comprehensions is a very powerful tool and it is
worth spending some time learning about.

Some tutorial links:

http://www.secnetix.de/~olli/Python/...rehensions.haw

http://www.cosc.canterbury.ac.nz/~greg/python/listcomp/
Larry Bates
Syscon, Inc.

"Derek Basch" <db****@yahoo.com> wrote in message
news:ma*************************************@pytho n.org...

Hello,

Can anyone point me towards an article or explain
how to properly alter a list as well as iterate
on its items? For example:

input:

word = ["albert", "likes", "surfing!"]

for word in sentence:
word += "foo"

result:

word = ["albertfoo", "likesfoo", "surfingfoo"]

Thanks,
Derek Basch



__________________________________
Do you Yahoo!?
Friends. Fun. Try the all-new Yahoo! Messenger.
http://messenger.yahoo.com/

[Peter Abel]

Derek Basch <db****@yahoo.com> wrote in message news:<ma*************************************@pyth on.org>...

Hello,

Can anyone point me towards an article or explain
how to properly alter a list as well as iterate
on its items? For example:

input:

word = ["albert", "likes", "surfing!"]

for word in sentence:
word += "foo"

result:

word = ["albertfoo", "likesfoo", "surfingfoo"]

Thanks,
Derek Basch

..
..
..

An solution No. 992345739219242.... is:-):

from operator import add
word = ["albert", "likes", "surfing!"]
map(add,word,['foo']*len(word)) ['albertfoo', 'likesfoo', 'surfing!foo']

Regards
Peter

[Peter Otten]

Derek Basch wrote:

Can anyone point me towards an article or explain
how to properly alter a list as well as iterate
on its items? For example:

input:

word = ["albert", "likes", "surfing!"]

for word in sentence:
word += "foo"

result:

word = ["albertfoo", "likesfoo", "surfingfoo"]

Note that the solutions presented so far do *not* modify the list in place.
This is important if you keep references to the list elswhere. For example:

backup = sample = ["alpha", "beta", "gamma"]
sample = map(lambda x: x + ".suffix", sample)
sample is backup False sample = [x + ".suffix" for x in sample]
sample is backup False

Here are two ways to achieve inplace modification:
backup = sample = ["alpha", "beta", "gamma"]
for i, x in enumerate(sample): .... sample[i] = x + ".suffix"
.... sample is backup True
backup = sample = ["alpha", "beta", "gamma"]
sample[:] = [x + ".suffix" for x in sample]
sample is backup True

Here the [:] slice on the left makes the difference.

Peter