Programming Forums > Script Programming > Python

UnKnown X · Dec 10th, 2005, 1:19 PM

I read ColdDeath's (brilliant

) tutorial, and decided to give Python a shot. So I made a programme that finds a Fibonacci number a few hours ago. Then I decided to come back and try to make it read from and write the results to a file.

Now, I can't figure out how to make it read the last number! The numbers are saved like this:

(Toggle Plain Text)

and so on (including the last newline)

I tried this, but it didn't work. I'm not sure where or why it fails:

(Toggle Plain Text)

        k = 1
        while (f.seek(k * -1, 2)) != '\n':
            k += 1
        k -= 1
        f.seek((f.read())-(f.read()-k))
        b = int(f.read((f.read())-(f.read()-k)))
        k += 2
        while (f.seek(k * -1, 2)) != '\n':
            k += 1
        k -= 1
        f.seek((f.read())-(f.read()-k))
        a = int(f.read((f.read())-(f.read()-k)))
        f.seek(0, 2)

Cerulean · Dec 10th, 2005, 1:41 PM

I can't see any reason why you're doing all of this manual seeking and reading - this isn't C. Python lets you iterate over the lines in a file really easily:

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myFile = file("fibnumbers.txt")
for line in myFile:
    print line

This will go through each line in the file and print it. Simple eh?

UnKnown X · Dec 10th, 2005, 1:45 PM

Well, C++ is the only other language I know :p

But how can I make it stop at the last line and save that to a variable, then the second last line to another variable?

Cerulean · Dec 10th, 2005, 1:51 PM

Shove each line into a list and then access the last and second last elements in this list.

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lines = []
for line in myFile:
    lines.append(line)
lastItem = lines[-1]  # -1 refers to the last item in a list
secondLastItem = lines[-2] # -2 refers to the second last item in a list.. etc.

UnKnown X · Dec 10th, 2005, 1:55 PM

Thanks, I'll try that!

coldDeath · Dec 10th, 2005, 1:57 PM

Unknown X, as Cerulean said, this is python not C.

Python has a completely different mindset to languages such as C.

I suggest reading "Dive into Python" (you can buy the book or read it for free at diveintopython.org)

UnKnown X · Dec 10th, 2005, 2:16 PM

Thanks for the link, coldDeath! I'll have a look now.

Yet another question: How would I make it write the line number next to the fibonacci number, and then ignore it (the line number)?
I.e:

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1: 1
2: 1
3: 2
4: 3
5: 5
6: 8
7: 13
8: 21
9: 34
...

Arevos · Dec 10th, 2005, 3:40 PM

Quote:

Originally Posted by UnKnown X

Yet another question: How would I make it write the line number next to the fibonacci number, and then ignore it (the line number)?
I.e:

(Toggle Plain Text)

1: 1
2: 1
3: 2
4: 3
5: 5
6: 8
7: 13
8: 21
9: 34
...

I'm not quite sure what you mean. Is the above "code" meant as input from a file, or output from your python program?

To output it, you can use the enumerate function, which encodes a running count into any sequence:

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for number, line in enumerate(file):
   print "%d: %s" % (number, line),

To input it, you can use the split function, which divides a string based on a specified delimiting character:

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for line in file:
   number, data = line.split(":")

UnKnown X · Dec 10th, 2005, 4:14 PM

It works perfectly! Thanks!

Dec 10th, 2005, 1:19 PM	#1
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Reading numbers from file I read ColdDeath's (brilliant ) tutorial, and decided to give Python a shot. So I made a programme that finds a Fibonacci number a few hours ago. Then I decided to come back and try to make it read from and write the results to a file. Now, I can't figure out how to make it read the last number! The numbers are saved like this: (Toggle Plain Text) 1 1 2 3 5 8 13 21 34 55 1 1 2 3 5 8 13 21 34 55 and so on (including the last newline) I tried this, but it didn't work. I'm not sure where or why it fails: (Toggle Plain Text) k = 1 while (f.seek(k * -1, 2)) != '\n': k += 1 k -= 1 f.seek((f.read())-(f.read()-k)) b = int(f.read((f.read())-(f.read()-k))) k += 2 while (f.seek(k * -1, 2)) != '\n': k += 1 k -= 1 f.seek((f.read())-(f.read()-k)) a = int(f.read((f.read())-(f.read()-k))) f.seek(0, 2) k = 1 while (f.seek(k * -1, 2)) != '\n': k += 1 k -= 1 f.seek((f.read())-(f.read()-k)) b = int(f.read((f.read())-(f.read()-k))) k += 2 while (f.seek(k * -1, 2)) != '\n': k += 1 k -= 1 f.seek((f.read())-(f.read()-k)) a = int(f.read((f.read())-(f.read()-k))) f.seek(0, 2)

Dec 10th, 2005, 1:41 PM	#2
Cerulean Professional Programmer Join Date: Apr 2005 Location: London, England Posts: 459 Rep Power: 4	I can't see any reason why you're doing all of this manual seeking and reading - this isn't C. Python lets you iterate over the lines in a file really easily: (Toggle Plain Text) myFile = file("fibnumbers.txt") for line in myFile: print line myFile = file("fibnumbers.txt") for line in myFile: print line This will go through each line in the file and print it. Simple eh?

Dec 10th, 2005, 1:51 PM	#4
Cerulean Professional Programmer Join Date: Apr 2005 Location: London, England Posts: 459 Rep Power: 4	Shove each line into a list and then access the last and second last elements in this list. (Toggle Plain Text) lines = [] for line in myFile: lines.append(line) lastItem = lines[-1] # -1 refers to the last item in a list secondLastItem = lines[-2] # -2 refers to the second last item in a list.. etc. lines = [] for line in myFile: lines.append(line) lastItem = lines[-1] # -1 refers to the last item in a list secondLastItem = lines[-2] # -2 refers to the second last item in a list.. etc.

Dec 10th, 2005, 1:57 PM	#6
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	Unknown X, as Cerulean said, this is python not C. Python has a completely different mindset to languages such as C. I suggest reading "Dive into Python" (you can buy the book or read it for free at diveintopython.org) __________________ Programming Tutorials - Linux Installation Guide - Learn Python - Learn C++ Got Slack? Join us at #programmingforums @ irc.freenode.net! My software never has bugs. It just develops random features.

Dec 10th, 2005, 2:16 PM	#7
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Thanks for the link, coldDeath! I'll have a look now. Yet another question: How would I make it write the line number next to the fibonacci number, and then ignore it (the line number)? I.e: (Toggle Plain Text) 1: 1 2: 1 3: 2 4: 3 5: 5 6: 8 7: 13 8: 21 9: 34 ... 1: 1 2: 1 3: 2 4: 3 5: 5 6: 8 7: 13 8: 21 9: 34 ...

Dec 10th, 2005, 1:45 PM	#3
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Well, C++ is the only other language I know :p But how can I make it stop at the last line and save that to a variable, then the second last line to another variable?

Dec 10th, 2005, 1:55 PM	#5
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Thanks, I'll try that!

Dec 10th, 2005, 4:14 PM	#9
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	It works perfectly! Thanks!

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Programming Forums > Script Programming > Python

Reading numbers from file