Running a for loop in python

Question

I'm trying to generate 1000 new files from already existing 1000 files in a folder named as 'mdp' into a new folder 'mdb', changing couple of lines in each of the original 1000 files. I took some help from overflow and @bruno desthuilliers suggested me to use this particular code but it hasn't worked yet and it says dest.write(line) AttributeError: 'str' object has no attribute 'write'. I'm kind of new to programming. Could anyone please tell me what am I missing?

     import os
     sourcedir = "/home/abc/xyz/mdp/"
     destdir = "/home/abc/xyz/mdb/"

     for filename in os.listdir(sourcedir):
       if not filename.endswith(".mdp"):
       continue

       source = os.path.join(sourcedir, filename)
       dest = os.path.join(destdir, filename)

     fin = open("/home/abc/xyz/mdp/md_1.mdp")
     fout = open("/home/abc/xyz/mdb/md_1.mdp", "w")
     for line in source:
     line = line.replace('integrator               = md', 'integrator               = md-vv')
     line = line.replace('dt                       = 0.001', 'dt                      = 
    -0.001')
     dest.write(line)

are you sure about the indentation ??? this is very critical in python.. the for loop indentation doesn't seem to be correct — mlwn
– mlwn, Commented Mar 26, 2020 at 17:18

frost-nzcr4 · Accepted Answer · 2020-03-26 17:32:28Z

1

You messed up with path (which str) and file objects (which a readable/writable), so you've to fix a bit your code:

with open(source) as fin, open(dest, "w") as fout:
    for line in fin:
        fout.write(
            line.replace(
                'integrator               = md',
                'integrator               = md-vv',
            ).replace(
                'dt                       = 0.001',
                'dt                      = -0.001',
            )
        )

also use with to properly close opened files in case of runtime errors.

edited Mar 26, 2020 at 17:32

answered Mar 26, 2020 at 17:19

frost-nzcr4

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Comments

EnriqueBet · Accepted Answer · 2020-03-26 18:23:27Z

1

The problem is that dest is a string, not an instance of an open file. The code that I modified should work. Please give it a try and let me know how does it go!

import os

sourcedir = "/home/abc/xyz/mdp/"
destdir = "/home/abc/xyz/mdb/"

for filename in os.listdir(sourcedir):
    if not filename.endswith(".mdp"):
        continue

    # Gets the fullpath for the source and dest files
    source = os.path.join(sourcedir, filename)
    dest = os.path.join(destdir, filename)

    # Open the files in read and write mode
    fin = open(source,"r")
    fout = open(dest, "w")

    # Creates a list of the lines contained in the 'dest' file
    lines = fin.readlines()

    # Close the source file as is no longer needed
    fin.close()

    # Loop over each line to implement the modifications
    for line in lines:
        line = line.replace('integrator               = md', 'integrator               = md-vv')
        line = line.replace('dt                       = 0.001', 'dt                      = 
    -0.001')
        # Writes the replaced line into the 'dest' file
        fout.write(line)

    # Close the 'dest' file after finishing looping
    fout.close()

Also, the code that you posted has some indentation issues, I fixed them here.

edited Mar 26, 2020 at 18:23

answered Mar 26, 2020 at 17:20

EnriqueBet

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2 Comments

accidental_coder Over a year ago

Thanks @EnriqueBet. This is giving me a similar error. fin = source.readlines() AttributeError: 'str' object has no attribute 'readlines'

accidental_coder Over a year ago

Still did not work, it created just one file which was md_863.mdp which was also blank. Am I supposed to actually state the source in the 7th line of this code in place of sourcedir?

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