Anders Andersson wrote:
I want to concatinate (I apologize for bad English, but it is not my native language) a list of strings to a string. I could use (I think):
s = "" map(lambda x: s.append(x), theList)
But I want to do something like (I think that the code above is clumsy):
s = reduce("concatinating function", theList, "")
And here is the questions: What to replace "concatinating function" with? Can I in some way give the +-operator as an argument to the reduce function? I know operators can be sent as arguments in Haskell and since Python has functions as map, filter and listcomprehension etc. I hope it is possible in Python too. In Haskell I would write:
You are looking for "import operator", followed by a use of operator.add in the reduce() call. Note, however, that you cannot add different types (generally) together, so you will run into trouble if you take the "naive" approach and just trying concatenating the strings and the list as you show above. Instead, you will need to pass the sequence of things through a call to map(str, sequence) first, to call the str() method on everything and make sure you are adding strings together. Thus:
import operator s = reduce(operator.add, map(str, theList))
or something like that.
However, none of this is considered the best approach these days, with the advent of list comprehensions and generator expressions. Here's the old approach (shown above) and the shiny new modern Pythonic approach (requires Python 2.4):
>>> theList = range(10) >>> import operator >>> reduce(operator.add, map(str, theList)) '0123456789' >>> ''.join(str(x) for x in theList) '0123456789'
-Peter
Thank you for replaying. The operator.add is new to me and I will keep it in mind. It will perhaps come to use. I will use the join function since it looks more beatiful!
-- Anders Andersson -- http://mail.python.org/mailman/listinfo/python-list
