python Read and Write csv File Instance Code

Python reading and writing CSV files requires importing CSV module of Python, and then reading and writing CSV files through functions csv. reader () and csv. writer () in CSV module.

Write to an CSV file

import csv   #  Need import csv File package of 

out=open("aa.csv",'wb')     #  Note that if you use ' w' Open in the form, and there will be more data in the middle every time you write it 1 A blank line, so use ' wb'

csv_write=csv.write(out,dialect='excel')

#  Let's write the specific content below 

ss=['a',3]

csv_write.writerow(ss)   # In this way ss The information inside is written to the aa.csv File, and it is in two columns 

                # Here, if you need to write more than one line, you can use a loop for loop input 

out.close()

Read the CSV file

import csv

out=open("aa.csv",'r')

read_csv=csv.reader(out,dialect='excel')

for line in read_csv:   # Cyclic output csv All data in the 

  print line

out.close()

Extension of knowledge points:

import csv

Read a file

reader method

with open('./data.csv', 'r') as f:
 reader = csv.reader(f)
 # python 2
 header = reader.next()
 # python 3x  Use python Built-in next
 header = next(reader)
 # Get the real data 
 for row in reader:
  print(row) #  Print every 1 Row, list type, indexed only by position 

A brief introduction to the next (iterable, [default]) function, which is a built-in python3x method for traversing iterative objects, where iterable can make strings, lists, dictionaries, ancestors, collections, etc. If default is given, this value is returned at the end of traversal, otherwise, an exception is thrown.
This reminds me of the dictionary's get () method, which has a similar effect. For example,

#  If dic There is no inside key1 This key, then we return the specified 0
dic.get('key1', 0)

DictReader method

Write a file

Corresponding to reading, there are also two methods for writing

writer method, list of applicable lists

 with open('./data.csv', 'w') as f:
  header = ['col1', 'col2', ...]
  writer = csv.writer(f)
  writer.writeheader(header)
  for row in row_list:
   writer.writerow(row)
  #  Or call directly 
  writer.writerows(row_list)
 

DictWriter method, applicable dictionary list

 with open('./data.csv', 'w') as f:
  dictwriter = csv.DictWriter(f)
  dictwriter.writeheader(dic_list[0].keys())
  for dic in dic_list:
   writer.writerow(dic)
  #  Or 1 Secondary write, call directly 
   wrier.writerows(dic_list)

They are all basic operations, so record 1 here. If you find it helpful, so much the better.