Question

I am reading a csv into a list, and I need to delete an entire line from the list under a specific condition:

import csv

thefile = []

def dowork():
    sourceFile='e.csv'
    CleanFile(sourceFile)

def CleanFile(sourceFile):
    global thefile
    thefile=list(csv.reader(open(sourceFile, 'rb'), delimiter=',', quotechar='"'))
    for line in thefile:
        if line[3]=='':
            #here's where i need to delete line from thefile

how would i delete line from thefile?

Answer 1

You need the index of line within thefile. Once you have that, it’s easy. And the way you get that is with enumerate.

def CleanFile(sourceFile):
    global thefile
    thefile=list(csv.reader(open(sourceFile, 'rb'), delimiter=',', quotechar='"'))
    for i, line in enumerate(thefile):
        if line[3]=='':
            del thefile[i]

However, it’s worth asking whether you actually need to delete it. For example, could you just filter it out like this?

def CleanFile(sourceFile):
    global thefile
    thefile=[line for line in 
             csv.reader(open(sourceFile, 'rb'), delimiter=',', quotechar='"')) 
             if line[3] != '']

Or, depending on what you’re doing with the data, maybe it makes even more sense to just skip over lines where line[3] == '' at output or calculation time. Or, even better, don’t make a list in the first place; just leave csv.reader as an iterator—then you can stick a filter in front of it via itertools.ifilter, or a generator expression. In fact, that’s as simple as just changing two characters:

def CleanFile(sourceFile):
    global thefile
    thefile=(line for line in 
             csv.reader(open(sourceFile, 'rb'), delimiter=',', quotechar='"')) 
             if line[3] != '')

Of course this makes no sense if you need, e.g., random access to thefile. But if you’re going to iterate over it line by line, this is probably the best solution. (Except that thefile shouldn’t be a global; it should be passed around from function to function as needed.)