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I have a test.txt file and by using python I want it to be read its each line into a list and after that I want to print another text file so that list number 3 comes first. I was not able to find any good examples so therefore I come here seeking for an answer from you all. Thanks in advance for any comments.
Here's a function that seems to do pretty-much what you want, not really very clearly written, but that's mostly cause I prefer maps and filters and such, a per-line-looping function with counters and such would, of course, work...
import string
DEFRECSEP = '================================='
DEFFIELDSEP = '\n'
DEFKEYSEP = ':'
def loadfile( filename,
recordsep = DEFRECSEP,
fieldsep= DEFFIELDSEP,
keysep=DEFKEYSEP
):
# read in whole file
tempdata = open( filename).read()
# break into records
tempdata = string.split( tempdata, recordsep )
# Get rid of extra whitespace
# and null records...
tempdata = filter( None, map( string.strip, tempdata ))
# for each record, get the field values
for i in range( len( tempdata)):
# split into the lines
fields = string.split( tempdata[i], fieldsep )
# strip trailing/leading whitespace
fields = map( string.strip, fields )
# get the key-value pairs
fields = map( string.split, fields, [ keysep ]*len(fields),
[1]*len(fields) )
# should probably do a strip here too...
tempdata[i] = fields
return tempdata
So, you get a structure that's like this
[
[
[key, value],
[key,value],
...
]
[
[key, value],
[key,value],
...
]
]
for record in dataset:
for key, value in record:
dosomething_with_key_and_value(key, value)
Incidentally, you'd probably find this kind of thing easier with a simple database module. Wouldn't be plain-text, but much easier (and faster) to use. If you really wanted convenience, you could even use shelve and just dump instances and/or data structures directly to disk so you don't need to do any parsing at all.
You can also try importing file data into Python arrays. The array module, documented at http://python.org/doc/current/lib/module-array.html might be of interest to you anyway, as well as the numeric python extensions at http://www.pfdubois.com/numpy/ .
You will have to manipulate the lines a bit to go from strings to integers. How to do this depends on what you want. If you want a nested list like
[[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
something like this should work:
arr = []
inp = open ("dat.txt","r")
#read line into array
for line in inp.readlines():
# add a new sublist
arr.append([])
# loop over the elemets, split by whitespace
for i in line.split():
# convert to integer and append to the last
# element of the list
arr[-1].append(int(i))
To get a flat list like
[1, 2, 3, 4, 5, 6, 7, 8, 9]
this might do:
arr = []
inp = open ("dat.txt","r")
#read line into array
for line in inp.readlines():
# loop over the elemets, split by whitespace
for i in line.split():
# convert to integer and append to the list
arr.append(int(i))
Hope this helps.
Depends on what you want to do. To append you can open it with "a":
If you want to preprend something you have to read from the file first:Code:with open("foo.txt", "a") as f:
f.write("new line\n")
To use the `with` statement in Python 2.5 you need to add "from __future__ import with_statement". Other than that, opening files with the `with` statement is definitely more readable and less error-prone than manual closing.Code:with open("foo.txt", "r+") as f:
old = f.read() # read everything in the file
f.seek(0) # rewind
f.write("new line\n" + old) # write the new line before