Python - How to loop through lines of multiple files

I have 2 files: "a.txt" and "b.txt" where I want to match lines between them. The files contain the following:

To match the lines, I'm doing the following

    a = open("a.txt","r") 

    b = open("b.txt","r")

    for al in a:

        al = al.split()

        val_a = al[0]

        for bl in b:

            bl = bl.split()

            val_b = bl[0]

            print val_a, val_b

Surprisingly, the print statement ONLY prints the following:

Which appears to be that the loop on a is only accessed once. What I tried for debugging is the following:

for al in a:

    al = al.split()

    val_a = al[0]

    print val_a

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

The print statement here prints all the values within a

Can someone help me with a possible explanation?

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

1

A similar question is answered over here

– Half Genius
Aug 2 '16 at 11:11

1

Also see stackoverflow.com/questions/13137969/…

– PM 2Ring
Aug 2 '16 at 11:17

I ended up using the "with" instead of the normal "open" statement which seems to work fine.

– ifreak
Aug 2 '16 at 13:31

add a comment |

I have 2 files: "a.txt" and "b.txt" where I want to match lines between them. The files contain the following:

To match the lines, I'm doing the following

    a = open("a.txt","r") 

    b = open("b.txt","r")

    for al in a:

        al = al.split()

        val_a = al[0]

        for bl in b:

            bl = bl.split()

            val_b = bl[0]

            print val_a, val_b

Surprisingly, the print statement ONLY prints the following:

Which appears to be that the loop on a is only accessed once. What I tried for debugging is the following:

for al in a:

    al = al.split()

    val_a = al[0]

    print val_a

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

The print statement here prints all the values within a

Can someone help me with a possible explanation?

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

1

A similar question is answered over here

– Half Genius
Aug 2 '16 at 11:11

1

Also see stackoverflow.com/questions/13137969/…

– PM 2Ring
Aug 2 '16 at 11:17

I ended up using the "with" instead of the normal "open" statement which seems to work fine.

– ifreak
Aug 2 '16 at 13:31

add a comment |

I have 2 files: "a.txt" and "b.txt" where I want to match lines between them. The files contain the following:

To match the lines, I'm doing the following

    a = open("a.txt","r") 

    b = open("b.txt","r")

    for al in a:

        al = al.split()

        val_a = al[0]

        for bl in b:

            bl = bl.split()

            val_b = bl[0]

            print val_a, val_b

Surprisingly, the print statement ONLY prints the following:

Which appears to be that the loop on a is only accessed once. What I tried for debugging is the following:

for al in a:

    al = al.split()

    val_a = al[0]

    print val_a

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

The print statement here prints all the values within a

Can someone help me with a possible explanation?

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

I have 2 files: "a.txt" and "b.txt" where I want to match lines between them. The files contain the following:

To match the lines, I'm doing the following

    a = open("a.txt","r") 

    b = open("b.txt","r")

    for al in a:

        al = al.split()

        val_a = al[0]

        for bl in b:

            bl = bl.split()

            val_b = bl[0]

            print val_a, val_b

Surprisingly, the print statement ONLY prints the following:

Which appears to be that the loop on a is only accessed once. What I tried for debugging is the following:

for al in a:

    al = al.split()

    val_a = al[0]

    print val_a

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

The print statement here prints all the values within a

Can someone help me with a possible explanation?

python file

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

edited Aug 2 '16 at 11:52

Half Genius

458621

edited Aug 2 '16 at 11:52

Half Genius

458621

edited Aug 2 '16 at 11:52

Half Genius

458621

asked Aug 2 '16 at 11:05

ifreak

69921436

asked Aug 2 '16 at 11:05

ifreak

69921436

asked Aug 2 '16 at 11:05

ifreak

69921436

1

A similar question is answered over here

– Half Genius
Aug 2 '16 at 11:11

1

Also see stackoverflow.com/questions/13137969/…

– PM 2Ring
Aug 2 '16 at 11:17

I ended up using the "with" instead of the normal "open" statement which seems to work fine.

– ifreak
Aug 2 '16 at 13:31

add a comment |

1

A similar question is answered over here

– Half Genius
Aug 2 '16 at 11:11

1

Also see stackoverflow.com/questions/13137969/…

– PM 2Ring
Aug 2 '16 at 11:17

I ended up using the "with" instead of the normal "open" statement which seems to work fine.

– ifreak
Aug 2 '16 at 13:31

A similar question is answered over here

– Half Genius
Aug 2 '16 at 11:11

Also see stackoverflow.com/questions/13137969/…

– PM 2Ring
Aug 2 '16 at 11:17

I ended up using the "with" instead of the normal "open" statement which seems to work fine.

– ifreak
Aug 2 '16 at 13:31

add a comment |

4 Answers
4

active

oldest

votes

You need to reset the file pointer to the start of the file for b.txt each time you attempt to loop through it, otherwise you've reached the end.

The easiest way to do this is with file.seek(0) as shown below:

a = open("a.txt","r") 

b = open("b.txt","r")

for al in a:

    al = al.split()

    val_a = al[0]



    b.seek(0)



    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

answered Aug 2 '16 at 11:10

moopet

4,51812333

add a comment |

You can fetch b to a list of lines with readlines(), and then you can iterate over it again and again:

a = open("a.txt","r") 

b = open("b.txt","r").readlines()

for al in a:

    al = al.split()

    val_a = al[0]

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

2

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

add a comment |

try this :

a = open("a.txt","r")

b = open("b.txt","r")

for i,j in zip(a,b):

    print (i.split()[0])

    print (j.split()[0])

Explanation:

1)zip file will open both files simultanously

2)for loop will loop through line by line (i=one line in a-file, j=one line in b-file)

3)i.split()[0] will give first word/element of line

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

add a comment |

Convert b as a list else first iteration through b will consume the file.

 blist= list(b)

Then the inner loop

For bl in blist:

 ...

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

add a comment |

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4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

You need to reset the file pointer to the start of the file for b.txt each time you attempt to loop through it, otherwise you've reached the end.

The easiest way to do this is with file.seek(0) as shown below:

a = open("a.txt","r") 

b = open("b.txt","r")

for al in a:

    al = al.split()

    val_a = al[0]



    b.seek(0)



    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

answered Aug 2 '16 at 11:10

moopet

4,51812333

add a comment |

You need to reset the file pointer to the start of the file for b.txt each time you attempt to loop through it, otherwise you've reached the end.

The easiest way to do this is with file.seek(0) as shown below:

a = open("a.txt","r") 

b = open("b.txt","r")

for al in a:

    al = al.split()

    val_a = al[0]



    b.seek(0)



    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

answered Aug 2 '16 at 11:10

moopet

4,51812333

add a comment |

You need to reset the file pointer to the start of the file for b.txt each time you attempt to loop through it, otherwise you've reached the end.

The easiest way to do this is with file.seek(0) as shown below:

a = open("a.txt","r") 

b = open("b.txt","r")

for al in a:

    al = al.split()

    val_a = al[0]



    b.seek(0)



    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

answered Aug 2 '16 at 11:10

moopet

4,51812333

You need to reset the file pointer to the start of the file for b.txt each time you attempt to loop through it, otherwise you've reached the end.

The easiest way to do this is with file.seek(0) as shown below:

a = open("a.txt","r") 

b = open("b.txt","r")

for al in a:

    al = al.split()

    val_a = al[0]



    b.seek(0)



    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

answered Aug 2 '16 at 11:10

moopet

4,51812333

answered Aug 2 '16 at 11:10

moopet

4,51812333

answered Aug 2 '16 at 11:10

moopet

4,51812333

answered Aug 2 '16 at 11:10

moopet

4,51812333

add a comment |

You can fetch b to a list of lines with readlines(), and then you can iterate over it again and again:

a = open("a.txt","r") 

b = open("b.txt","r").readlines()

for al in a:

    al = al.split()

    val_a = al[0]

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

2

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

add a comment |

You can fetch b to a list of lines with readlines(), and then you can iterate over it again and again:

a = open("a.txt","r") 

b = open("b.txt","r").readlines()

for al in a:

    al = al.split()

    val_a = al[0]

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

2

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

add a comment |

You can fetch b to a list of lines with readlines(), and then you can iterate over it again and again:

a = open("a.txt","r") 

b = open("b.txt","r").readlines()

for al in a:

    al = al.split()

    val_a = al[0]

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

You can fetch b to a list of lines with readlines(), and then you can iterate over it again and again:

a = open("a.txt","r") 

b = open("b.txt","r").readlines()

for al in a:

    al = al.split()

    val_a = al[0]

    for bl in b:

        bl = bl.split()

        val_b = bl[0]

        print val_a, val_b

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

edited Aug 2 '16 at 11:15

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

answered Aug 2 '16 at 11:08

Ohad Eytan

5,0471627

2

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

add a comment |

2

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

Depending on the size it is even better to read the lines of b once and for all

– Jean-François Fabre♦
Aug 2 '16 at 11:14

add a comment |

try this :

a = open("a.txt","r")

b = open("b.txt","r")

for i,j in zip(a,b):

    print (i.split()[0])

    print (j.split()[0])

Explanation:

1)zip file will open both files simultanously

2)for loop will loop through line by line (i=one line in a-file, j=one line in b-file)

3)i.split()[0] will give first word/element of line

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

add a comment |

try this :

a = open("a.txt","r")

b = open("b.txt","r")

for i,j in zip(a,b):

    print (i.split()[0])

    print (j.split()[0])

Explanation:

1)zip file will open both files simultanously

2)for loop will loop through line by line (i=one line in a-file, j=one line in b-file)

3)i.split()[0] will give first word/element of line

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

add a comment |

try this :

a = open("a.txt","r")

b = open("b.txt","r")

for i,j in zip(a,b):

    print (i.split()[0])

    print (j.split()[0])

Explanation:

1)zip file will open both files simultanously

2)for loop will loop through line by line (i=one line in a-file, j=one line in b-file)

3)i.split()[0] will give first word/element of line

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

try this :

a = open("a.txt","r")

b = open("b.txt","r")

for i,j in zip(a,b):

    print (i.split()[0])

    print (j.split()[0])

Explanation:

1)zip file will open both files simultanously

2)for loop will loop through line by line (i=one line in a-file, j=one line in b-file)

3)i.split()[0] will give first word/element of line

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

edited Mar 8 at 4:58

answered Aug 2 '16 at 11:14

Vaibhav

669416

answered Aug 2 '16 at 11:14

Vaibhav

669416

answered Aug 2 '16 at 11:14

Vaibhav

669416

add a comment |

Convert b as a list else first iteration through b will consume the file.

 blist= list(b)

Then the inner loop

For bl in blist:

 ...

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

add a comment |

Convert b as a list else first iteration through b will consume the file.

 blist= list(b)

Then the inner loop

For bl in blist:

 ...

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

add a comment |

Convert b as a list else first iteration through b will consume the file.

 blist= list(b)

Then the inner loop

For bl in blist:

 ...

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

Convert b as a list else first iteration through b will consume the file.

 blist= list(b)

Then the inner loop

For bl in blist:

 ...

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

answered Aug 2 '16 at 11:09

Jean-François Fabre♦

106k1057115

add a comment |

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