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Wim Feijen wrote:

> I was wondering, how to make a feature request?

You can post suggestions to improve python on the python-ideas mailing list
or make feature requests on the bugtracker at bugs.python.org

> I would really like having a string.contains('...') function which returns
> either True or False. I know I can mimick this behaviour by saying
> string.find('...') != -1 , however, I find this harder to read.
>
> string.contains('...') is easier to understand and more closely resembles
> natural language.

In modern python those functions provided by the string module that are also
available as methods should not be used anymore. Instead of

string.find(s, substr)

write

s.find(substr)

If you are not interested in the position of the substr use the "in"
operator:

if substr in s:
print "found"
else:
print "not found"

Peter

On 9/24/2010 4:21 AM, Peter Otten wrote:

>
> If you are not interested in the position of the substr use the "in"
> operator:
>
> if substr in s:
> print "found"
> else:
> print "not found"
>

Another "missing feature" candidate: sublist

>>> 'bc' in 'abcde'
True
>>> list('bc') in list('abcde')
False


A little Googling indicates that Haskell *does* have this feature: [1]


ghci> [2,6] `isInfixOf` [3,1,4,1,5,9,2,6,5,3,5,8,9,7,9]
True

I haven't located an equivalent Python idiom, though. I took a quick
look through numpy, but no luck. Can anyone help?

Tx,
John

[1] http://book.realworldhaskell.org/rea...ogramming.html

John Posner wrote:
> Another "missing feature" candidate: sublist
>
> >>> 'bc' in 'abcde'
> True
> >>> list('bc') in list('abcde')
> False

I'm not aware of any idioms, but how about a simple function?

def listinlist(list1, list2):
"checks if list1 is in list2"
if not list1:
return True
if not list2:
return False
length = len(list1)
pos = 0
while True:
try:
pos = list2.index(list1[0], pos)
except ValueError:
return False
if list2[posos+length] == list1:
return True
pos += 1

~Ethan~

On 09/24/10 13:01, Ethan Furman wrote:
> John Posner wrote:
>> Another "missing feature" candidate: sublist
>>
>> >>> 'bc' in 'abcde'
>> True
>> >>> list('bc') in list('abcde')
>> False
>
> I'm not aware of any idioms, but how about a simple function?
>
> def listinlist(list1, list2):
> "checks if list1 is in list2"
> if not list1:
> return True
> if not list2:
> return False
> length = len(list1)
> pos = 0
> while True:
> try:
> pos = list2.index(list1[0], pos)
> except ValueError:
> return False
> if list2[posos+length] == list1:
> return True
> pos += 1

Which I suppose could be rewritten something like

def listinlist(l1, l2):
len1 = len(l1)
offsets_to_consider = 1 + len(l2) - len1
return any(
l1 == l2[i:i+len1]
for i in xrange(offsets_to_consider)
)

Foldable into a one-line version if one's sick enough to use it:

list_in_list = lambda l1, l2: any(l1 == l2[i:i+len(l1)] for i
in range(1 + len(l2) - len(l1)))

-tkc

On 9/24/2010 2:45 PM, Tim Chase wrote:
> On 09/24/10 13:01, Ethan Furman wrote:
>> John Posner wrote:
>>> Another "missing feature" candidate: sublist
>>>
>>> >>> 'bc' in 'abcde'
>>> True
>>> >>> list('bc') in list('abcde')
>>> False
>>
>> I'm not aware of any idioms, but how about a simple function?

<snip>

>
> Foldable into a one-line version if one's sick enough to use it:

<snip>


Looking at this a bit more, I can see why the *in* operator applies to
strings, but not to lists. Consider the ambiguity in this
"heterogeneous" list:

mylist = [0, 1, 2, 3, [a, b], 10, 11, 12, a, b, 13]

Should the expression *[a, b] in mylist* get a hit at offset 4, or at
slice [8:10]?

If you know that your lists will be homogeneous ("scalar" values only),
or if you're willing to program around the potential ambiguity, then
Ethan's function can easily be adapted into a __contains__() method of a
*list* subclass.

Tx,
John