Using map function instead of for loop

Question

I want to find number of lines and words in a file. My input file "testfile.txt' has 6 lines and 23 words. For finding number of words I am using map() function instead of the for loop. When I executed this code it shows the memory location of the object instead of "23": Number of words =

What am I doing wrong here?

def wordcount(l):
    global numwords
    words = l.split()
    numwords += len(words)

f=open('testfile.txt')
lines = f.readlines()
numlines = len(lines)
print ('Number of lines =', numlines)

numwords=0

numwords = map(wordcount, lines)
print ('Number of words =', numwords)

Here is the answer I get "Number of words = <map object at 0x024DF0F0>". I am using Python 3.2 if it helps a bit. — Kalyan
– Kalyan, Commented Apr 12, 2011 at 9:51

user225312 · Accepted Answer · 2011-04-12 09:55:36Z

2

In Python 3, map is an iterator: (akin: itertools.imap)

class map(object)
 |  map(func, *iterables) --> map object
 |  
 |  Make an iterator that computes the function using arguments from
 |  each of the iterables.  Stops when the shortest iterable is exhausted.

While in Python 2:

map(...)
    map(function, sequence[, sequence, ...]) -> list

It returns a list by default.

So in your case, you need to do:

numwords = list(map(wordcount, lines))

There are other problems also with your code, but others have pointed that out well enough.

answered Apr 12, 2011 at 9:55

user225312

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Comments

Dan D. · Accepted Answer · 2011-04-12 09:54:23Z

2

after:

numwords = map(wordcount, lines)

numwords is a list of None the same length as lines as wordcount returns None

for line in lines:
    words = line.split()
    numwords += len(words)

would be better and more pythonic

answered Apr 12, 2011 at 9:54

Dan D.

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1 Comment

eumiro Over a year ago

+1, or in one line: numwords = sum(len(line.split()) for line in lines)

Sandro Munda · Accepted Answer · 2011-04-12 09:55:09Z

1

You should avoid to use a global variable like 'numwords'. You have to return numwords in your wordcount() function.

This code works :

def wordcount(l):
    numwords = 0
    words = l.split()
    numwords += len(words)
    return numwords

f = open('testfile.txt')
lines = f.readlines()
numlines = len(lines)
print('Number of lines =', numlines)

numwords = 0
numwords = map(wordcount, lines)
print ('Number of words =', numwords)

My testfile.txt contains :

Hello world
my name is
james bond

Ouput :

('Number of lines =', 3)
('Number of words =', [2, 3, 2])

answered Apr 12, 2011 at 9:55

Sandro Munda

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1 Comment

Lauritz V. Thaulow Over a year ago

Change the last line to print ('Number of words =', sum(numwords)) to get the grand total of words.

Gilliland · Accepted Answer · 2011-08-09 10:17:58Z

1

Read paragraphs to lines and ...

print 'Num of words =', reduce(lambda x,y: x+y ,[len(line.split()) for line in lines])

answered Aug 9, 2011 at 10:17

Gilliland

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Comments

Andrey Sboev · Accepted Answer · 2011-04-12 09:51:53Z

0

function wordcount doesn't return anything, write return numwords Now your function calcualates numwords and then return None by default, and you erase this global variable

answered Apr 12, 2011 at 9:51

Andrey Sboev

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1 Comment

Kalyan Over a year ago

Getting rid of "global declaration helped. Also I had to catch the function's output into a list as @sukhbir pointed out. Following code worked:def wordcount(l): numwords=0 words=l.split() numwords += len(words) return numwords file=open('testfile.txt') lines = file.readlines() print ('Number of lines =', len(lines)) numwords = list(map(wordcount,lines)) print ('Number of words =', sum(numwords))

Chris · Accepted Answer · 2011-04-12 09:59:56Z

0

Here you go, map either returns a list or iterator, so this modification will work in either case. (python2 vs python3)

def wordcount(l):
    global numwords
    words = l.split()
    numwords += len(words)

f=open('testfile.txt')
lines = f.readlines()
numlines = len(lines)
print ('Number of lines =', numlines)

numwords=0

numwords = map(wordcount, lines)
print ('Number of words =', len(list(numwords)))

answered Apr 12, 2011 at 9:59

Chris

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