Python for AI: A Crash Course
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Demo
In this demo, you’ll read and write CSV files. Just as you did in the demo for text files, you’ll first write some code to write a CSV file and then write code to read it.
Writing To a CSV File From a Collection of Lists
Write a new CSV file. Open the working-with-files-starter.ipynb notebook and scroll to the Working with CSV Files section.
import csv
with open('operating-systems.csv', 'w') as file:
writer = csv.writer(file)
# Write header row
writer.writerow(['operating_system', 'creator', 'year'])
# Write data rows
data_rows = [
["MS-DOS", "Microsoft", 1981],
["macOS", "Apple", 1984],
["Windows", "Microsoft", 1985],
["Linux", "Linus Torvalds", 1991],
]
writer.writerows(data_rows)
operating_system,creator,year
MS-DOS,Microsoft,1981
macOS,Apple,1984
Windows,Microsoft,1985
Linux,Linus Torvalds,1991
Reading a CSV File as a Collection of Lists
Now, write some code to read the CSV file that the previous code wrote. Run the following in a new code cell:
with open("operating-systems.csv", "r") as file:
reader = csv.reader(file)
for row in reader:
print(row)
['operating_system', 'creator', 'year']
['MS-DOS', 'Microsoft', '1981']
['macOS', 'Apple', '1984']
['Windows', 'Microsoft', '1985']
['Linux', 'Linus Torvalds', '1991']
Reading a CSV File as a Collection of Dictionaries
Use DictReader to read operating-systems.csv as a collection of dictionaries. This is possible because the file’s first line contains the column headers’ names.
with open("operating-systems.csv", "r") as file:
reader = csv.DictReader(file)
for row in reader:
print(row)
{'operating_system': 'MS-DOS', 'creator': 'Microsoft', 'year': '1981'}
{'operating_system': 'macOS', 'creator': 'Apple', 'year': '1984'}
{'operating_system': 'Windows', 'creator': 'Microsoft', 'year': '1985'}
{'operating_system': 'Linux', 'creator': 'Linus Torvalds', 'year': '1991'}
Writing To a CSV File From a List of Dictionaries
Finally, write the CSV version of the “programming languages” file you wrote for the text files demo. This will use DictReader’s counterpart, DictWriter, to write the file and the programming_languages list as the data source.
field_names = [
"name",
"creator",
"year_appeared",
"site_url",
"active",
]
with open("programming languages.csv", 'w') as file:
writer = csv.DictWriter(file, fieldnames=field_names)
writer.writeheader()
for row in programming_languages:
writer.writerow(row)
with open("programming languages.csv", "r") as file:
reader = csv.DictReader(file)
for row in reader:
print(row)
{'name': 'Python', 'creator': 'Guido van Rossum', 'year_appeared': '1991', 'site_url': 'https://www.python.org/', 'active': 'True'}
...