如何从CSV文件导入数据并将其存储在变量中？

Question

I am extremely new to python 3 and I am learning as I go here. I figured someone could help me with a basic question: how to store text from a CSV file as a variable to be used later in the code. So the idea here would be to import a CSV file into the python interpreter:

import csv
with open('some.csv', 'rb') as f:
    reader = csv.reader(f)
    for row in reader:
        ...

and then extract the text from that file and store it as a variable (ie w = ["csv file text"] ) to then be used later in the code to create permutations:

print (list(itertools.permutations(["w"], 2)))

If someone could please help and explain the process, it would be very much appreciated as I am really trying to learn. Please let me know if any more explanation is needed!

Answer 1

itertools.permutations() wants an iterable (eg a list) and a length as its arguments, so your data structure needs to reflect that, but you also need to define what you are trying to achieve here. For example, if you wanted to read a CSV file and produce permutations on every individual CSV field you could try this:

import csv
with open('some.csv', newline='') as f:
    reader = csv.reader(f)
    w = []
    for row in reader:
        w.extend(row)

print(list(itertools.permutations(w, 2)))

The key thing here is to create a flat list that can be passed to itertools.permutations() - this is done by intialising w to an empty list, and then extending its elements with the elements/fields from each row of the CSV file.

Note : As pointed out by @martineau, for the reasons explained here , the file should be opened with newline='' when used with the Python 3 csv module.

Answer 2

If you want to use Python 3 (as you state in the question) and to process the CSV file using the standard csv module, you should be careful about how to open the file. So far, your code and the answers use the Python 2 way of opening the CSV file. The things has changed in Python 3.

As shengy wrote, the CSV file is just a text file, and the csv module gets the elements as strings. Strings in Python 3 are unicode strings. Because of that, you should open the file in the text mode, and you should supply the encoding. Because of the nature of CSV file processing, you should also use the newline='' when opening the file.

Now extending the explanation of Burhan Khalid ... When reading the CSV file, you get the rows as lists of strings. If you want to read all content of the CSV file into memory and store it in a variable, you probably want to use the list of rows (ie list of lists where the nested lists are the rows). The for loop iterates through the rows. The same way the list() function iterates through the sequence (here through the sequence of rows) and build the list of the items. To combine that with the wish to store everything in the content variable, you can write:

import csv

with open('some.csv', newline='', encoding='utf_8') as f:
    reader = csv.reader(f)
    content = list(reader)

Now you can do your permutation as you wish. The itertools is the correct way to do the permutations.

Answer 3

import csv
data = csv.DictReader(open('FileName.csv', 'r'))
print data.fieldnames
output = []
for each_row in data:
   row = {}
   try:
     p = dict((k.strip(), v) for k, v in p.iteritems() if v.lower() != 'null')
   except AttributeError, e:
     print e
     print p
     raise Exception()
//based on the number of column   
if p.get('col1'):
    row['col1'] = p['col1']
if p.get('col2'):
    row['col2'] = p['col2']
output.append(row)

Finally all data stored in output variable

Answer 4

Is this what you need?

import csv
with open('some.csv', 'rb') as f:
    reader = csv.reader(f, delimiter=',')
    rows = list(reader)

print('The csv file had {} rows'.format(len(rows)))

for row in rows:
   do_stuff(row)

do_stuff_to_all_rows(rows)

The interesting line is rows = list(reader) , which converts each row from the csv file (which will be a list), into another list rows , in effect giving you a list of lists.

If you had a csv file with three rows, rows would be a list with three elements, each element a row representing each line in the original csv file.

Answer 5

If all you care about is to read the raw text in the file ( csv or not) then:

with open('some.csv') as f:
    w = f.read()

will be a simple solution to having w="csv, file, text\\nwithout, caring, about columns\\n"

Answer 6

First, a csv file is a text file too, so everything you can do with a file, you can do it with a csv file. That means f.read() , f.readline() , f.readlines() can all be used. see detailed information of these functions here .

But, as your file is a csv file, you can utilize the csv module.

# input.csv
# 1,david,enterprise
# 2,jeff,personal

import csv

with open('input.csv') as f:
    reader = csv.reader(f)
    for serial, name, version in reader:
        # The csv module already extracts the information for you
        print serial, name, version

More details about the csv module is here .

Answer 7

You should try pandas, which work both with Python 2.7 and Python 3.2+ :

import pandas as pd
csv = pd.read_csv("your_file.csv")

Then you can handle you data easily.

More fun here