使用CSV模型从较大文件中提取特定行的文本

Question

So I'm extracting the lines that I want from this larger file using this program:

import csv

name = ['NAMETHEFIRST,' 'NAMEANOTHERNAME ']
data = csv.reader(open('C:\\bigfile.csv'))

with open('C:\\smalldataset.xcl','w') as outf:
    csv.writer(outf).writerows(l for l in data if l[0] in name)

The program runs. However I am only getting the line of data from NAMETHEFIRST and I get no data from NAMETHEOTHERNAME written to my small dataset file. This works exactly as I want printing all relevant info from the large data set of the line of data for NAME THE FIRST but i get no information from the second nametheother name written to the smaller file. Why isn't this working?

Answer 1

This is a list with one string:

['NAMETHEFIRST,' 'NAMEANOTHERNAME ']

This is a list with two strings:

['NAMETHEFIRST', 'NAMEANOTHERNAME ']

Note the placement of the comma.

Also note that your second string has a space at the end.

Answer 2

This line of code

name = ['NAMETHEFIRST,' 'NAMEANOTHERNAME ']

is equivalent to

name = ['NAMETHEFIRST,NAMEANOTHERNAME ']

because Python follows C in concatenating adjacent string constants at compile time.

You say """I am only getting the line of data from NAMETHEFIRST and I get no data from NAMETHEOTHERNAME written to my small dataset file""" -- however the code that you show will NOT produce that result ; it will select only lines that start with

"NAMETHEFIRST,NAMEANOTHERNAME ", 

You will get the stated result only if that line is actually:

name = ['NAMETHEFIRST', 'NAMEANOTHERNAME ']

and that is presumably because the second name in the file doesn't have a trailing space as above.

Other problems:

csv.writer(outf).writerows(l for l in data if l[0] in name) is trying to be a bit too clever. If you break it down into bite-size chunks, you can much more easily use a debugger or just print statements to show you what is actually happening.

Try this:

print len(name), name
data = csv.reader(open('C:\\bigfile.csv', 'rb')) # ALWAYS open csv files in BINARY mode
with open('C:\\smalldataset.xcl','wb') as outf: # ALWAYS open csv files in BINARY mode
    writer = csv.writer(outf)
    for row_index, row in enumerate (data): # don't use 'l' as a variable name
        print row_index + 1, row
        if row[0] in name:
            writer.writerow(row)