Deleting rows in a file using Python - python-2.7

Question

I have input files "input.dat" contain some values like this :
41611 2014 12 18 0 0
41615 2014 12 18 0 0
41625 2014 12 18 0 0
41640 2014 6 14 3 3
42248 2014 12 18 0 0
42323 2014 12 18 0 0
42330 2014 8 13 7 7
42334 2014 12 18 0 0
42335 2014 12 18 0 0
...
I have many dataset files but seems so many unwanted data
How to delete many rows for this case 41640 and 42330 and its entire row values at instant. For now I used this script:
with open(path+fname,"r") as input:
with open("00-new.dat","wb") as output:
for line in input:
if line!="41640"+"\n":
output.write(line)
The result: The data 41640 is still exist in output. Any ideas??

Answer 1

You need to change your condition - how it is now it checks if the whole line is equal to 41640. Each line is instead equal to the whole row of data you are reading followed by a \n. Fixed version of your program looks like this:
with open("00-old.dat","r") as input:
with open("00-new.dat","wb") as output:
for line in input:
if "41640" not in line:
output.write(line)
To delete multiple lines you can use all() combined with a list comprehension as for instance described in this post,
if all(nb not in line for nb in del_list):
output.write(line)
where del_list is a list of values you want deleted,
del_list = ["41615", "41640", "42334"]
Also, due to Python's operator precedence your original condition will always evaluate to True. That is because even if the 41640!=line was false, the \n is added to it and interpreted (after conversion) as True. Basically, the != is evaluated first, instead of the string concatenation followed by a !=.