python - TypeError: str object is not an iterator -

i have file consisting of words, 1 word on each line. file looks this:

aaa bob fff err ddd fff err 

i want count frequency of pair of words occur 1 after other.

for example,

aaa,bob: 1 bob,fff:1 fff,err:2 

and on. have tried this

f=open(file,'r') content=f.readlines() f.close() dic={} it=iter(content) line in content:     print line, next(line);     dic.update({[line,next(line)]: 1}) 

i got error:

typeerror: str object not iterator 

i tried using iterator:

it=iter(content) x in it:     print x, next(x); 

got same error again. please help!

you need keep track of previous line, file object returns own iterator don't need iter or readlines @ all, call next once @ start creating variable prev keep updating prev in loop:

from collections import defaultdict  d = defaultdict(int)  open("in.txt") f:     prev = next(f).strip()     line in map(str.strip,f): # python2 use itertools.imap         d[prev, line] += 1         prev = line 

which give you:

defaultdict(<type 'int'>, {('aaa', 'bob'): 1, ('fff', 'err'): 2, ('err', 'ddd'): 1, ('bob', 'fff'): 1, ('ddd', 'fff'): 1})