Need to read specific range of text file in Python
I need to read a text file after specific line let say line # 100. This line has specific number such as '255'. Then i want to read next 500 lines using for loop. in those 500 line i have some numbers to extract. Such as in P[3] position. Then I need to pass those value into an array. At the end I should have few sets like below. I used following code to do that. But i failed. Can any one help me.
File looks like below
Generated by trjconv : a bunch of waters t= 0.00000
500
1SOL OW 1 1.5040 2.7580 0.6820
2SOL OW 4 1.5210 0.9510 2.2050
500SOL OW 2998 1.5310 1.7952 2.1981
3.12736 3.12736 3.12736
Generated by trjconv : a bunch of waters t= 9000.00000
500
1SOL OW 1 1.5040 2.7580 0.6820
2SOL OW 4 1.5210 0.9510 2.2050
500SOL OW 2998 1.5310 1.7952 2.1981
3.10941 3.10941 3.10941
Generated by trjconv : a bunch of waters t= 0.00000
500
1SOL OW 1 1.5040 2.7580 0.6820
2SOL OW 4 1.5210 0.9510 2.2050
500SOL OW 2998 1.5310 1.7952 2.1981
3.12736 3.12736 3.12736
Generated by trjconv : a bunch of waters t= 9000.00000
500
1SOL OW 1 1.5040 2.7580 0.6820
2SOL OW 4 1.5210 0.9510 2.2050
500SOL OW 2998 1.5310 1.7952 2.1981
3.10941 3.10941 3.10941
Coding I have written
F = open('Data.gro', 'r')
A = open('XYZ.txt', 'w')
XO = []
I = range(1,500)
for line in F:
P = line.split()
if P[0] == '256': # after i found this I want to read next five hundred lines.
for R in I:
P = line.split()
XO.append(P[3])
R +=1
# after the for loop I want write 'XO' in to file as set 01 then should go to next P[0] == '256'
Results should be like below in file name 'XYZ.txt'
Set 01
X = [1.32, 4.132, 2.23, .... upto 500]
Set 02
X = [4.232, 1.162, 3.73, .... upto 500]
You just need to fetch the lines inside the inner loop as well, you can use next() for that:
with open('filename') as f:
for line in f:
if line.split()[0] == '256':
for _ in xrange(500):
line = next(f)
#do something with line
In the above code you'll get a StopIteration error if the file doesn't have 500 lines after the condition is True, you can handle that either using a try-except or take a slice of the file object using itertools.islice :
from itertools import islice
with open('filename') as f:
for line in f:
if line.split()[0] == '256':
XO =[line.split(None, 4)[3] for line in islice(f, 500)]
#Write XO to a file
If the lines don't start with leading spaces then you can use @zhangxaochen suggestion to replace the line.split()[0] == '256' part with line.startswith('256 ') . Another option is to use line.split(None, 1)[0] == '256' , which is going to split the line only once.
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