Python将整数从csv文件读取到列表中

Question

I am having some trouble trying to read a particular column in a csv file into a list in Python. Below is an example of my csv file:

Col 1       Col 2
1,000,000   1
  500,000   2
  250,000   3

Basically I am wanting to add column 1 into a list as integer values and am having a lot of trouble doing so. I have tried:

for row in csv.reader(csvfile):
    list = [int(row.split(',')[0]) for row in csvfile]

However, I get a ValueError that says "invalid literal for int() with base 10: '"1'

I then tried:

for row in csv.reader(csvfile):
    list = [(row.split(',')[0]) for row in csvfile]

This time I don't get an error however, I get the list:

['"1', '"500', '"250']

I have also tried changing the delimiter:

for row in csv.reader(csvfile):
    list = [(row.split(' ')[0]) for row in csvfile]

This almost gives me the desired list however, the list includes the second column as well as, "\\n" after each value:

['"1,000,000", 1\n', etc...]

If anyone could help me fix this it would be greatly appreciated!

Cheers

Answer 1

You can open the file and split at the space using regular expressions:

import re
file_data = [re.split('\s+', i.strip('\n')) for i in open('filename.csv')]
final_data = [int(i[0]) for i in file_data[1:]]

Answer 2

You should choose your delimiter wisely : If you have floating numbers using . , use , delimiter, or if you use , for floating numbers, use ; as delimiter.

Moreover, as referred by the doc for csv.reader you can use the delimiter= argument to define your delimiter, like so:

with open('myfile.csv', 'r') as csvfile:
    mylist = []
    for row in csv.reader(csvfile, delimiter=';'):
        mylist.append(row[0]) # careful here with [0]

or short version:

with open('myfile.csv', 'r') as csvfile:
    mylist = [row[0] for row in csv.reader(csvfile, delimiter=';')]

To parse your number to a float, you will have to do

 float(row[0].replace(',', ''))

Answer 3

First of all, you must parse your data correctly. Because it's not, in fact, CSV (Comma-Separated Values) but rather TSV (Tab-Separated) of which you should inform CSV reader (I'm assuming it's tab but you can theoretically use any whitespace with a few tweaks):

for row in csv.reader(csvfile, delimiter="\t"):

Second of all, you should strip your integer values of any commas as they don't add new information. After that, they can be easily parsed with int() :

int(row[0].replace(',', ''))

Third of all, you really really should not iterate the same list twice. Either use a list comprehension or normal for loop, not both at the same time with the same variable. For example, with list comprehension:

csvfile = StringIO("Col 1\tCol 2\n1,000,000\t1\n500,000\t2\n250,000\t3\n")
reader = csv.reader(csvfile, delimiter="\t")
next(reader, None)  # skip the header
lst = [int(row[0].replace(',', '')) for row in reader]

Or with normal iteration:

csvfile = StringIO("Col 1\tCol 2\n1,000,000\t1\n500,000\t2\n250,000\t3\n")
reader = csv.reader(csvfile, delimiter="\t")
lst = []
for i, row in enumerate(reader):
    if i == 0:
        continue  # your custom header-handling code here
    lst.append(int(row[0].replace(',', '')))

In both cases, lst is set to [1000000, 500000, 250000] as it should. Enjoy.

By the way, using reserved keyword list as a variable is an extremely bad idea.

UPDATE. There's one more option that I find interesting. Instead of setting the delimiter explicitly you can use csv.Sniffer to detect it eg:

csvdata = "Col 1\tCol 2\n1,000,000\t1\n500,000\t2\n250,000\t3\n"
csvfile = StringIO(csvdata)
dialect = csv.Sniffer().sniff(csvdata)
reader = csv.reader(csvfile, dialect=dialect)

and then just like the snippets above. This will continue working even if you replace tabs with semicolons or commas (would require quotes around your weird integers) or, possibly, something else.