Printing duplicates from a text file

[pystarter]

If i have a text file 'test.txt' containing:

1
1
1
2
2
3

I want it to print all the lines that are duplicates/matches.

So I would expect an output of

1
1
1
2
2

I was thinking something along the lines of:

test = open("test.txt", 'r')
 
for x in test:
     for y in test:
         if x==y:
            print x
            print y

But it doesn't work.

Please can someone advise?

[bvdet]

Read the file and compile a list of the items in the file.
Iterate on the list.
Use list method count to determine if there are duplicates.

Example:

>>> seq = ['1', '1', '2', '2', '2', '3']
>>> for item in seq:
...     if seq.count(item) > 1:
...         print item
...         
1
1
2
2
2
>>> 

[dwblas]

For larger files, store the records found in a set so you only iterate once.

x_set=set()
for x in test:
    x=x.strip()
    if x in x_set:
        print x
    else:
        x_set.add(x) 

The code you posted would iterate over the list once for each successive record and would be written:

test = open("test.txt", 'r')
 
all_recs=test.readlines()
test.close()
 
for ctr in range(len(all_recs)):
    x = all_recs[ctr].strip()
    for y in range(ctr+1, len(all_recs):  ## start with the next record
        if x==all_recs[y].strip():
            print y, all_recs[y] 

[pystarter]

Thanks guys - great help!