CVS Files
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Instruction
Spreadsheets weren’t designed as databases. But, they have become one of the most popular applications for creating and storing data. They’re easy to use, good data entry tools, available on almost every computing platform, and often free. They enable users to perform calculations, analyze, and visualize data. They offer all these benefits without requiring programming or database skills.
Basic CSV File Reading
To work with CSV data, you need to import the csv module, which is part of the Python Standard Library.
import csv
with open("some-file.csv", "r") as file:
reader = csv.reader(file)
for row in reader:
print(row)
browser,vendor,year_appeared
Chrome,Google,2008
Safari,Apple,2003
Edge,Microsoft,2015
['browser', 'vendor', 'year_appeared']
['Chrome', 'Google', '2008']
['Safari', 'Apple', '2003']
['Edge', 'Microsoft', '2015']
Basic CSV File Writing
Reading a CSV file involves creating a file object and then passing it to csv.reader(). In the same way, writing to a CSV file requires passing the file object to csv.writer(). This creates a CSV writer object that writes to the file in CSV format.
one,two
three,four
import csv
with open("some-other-file.csv", "w") as file:
writer = csv.writer(file)
# Write header row
writer.writerow([
"browser",
"vendor",
"year_appeared"
])
# Write data rows
data_rows = [
["Chrome", "Google", 2008],
["Safari", "Apple", 2003],
["Edge", "Microsoft", 2015]
]
writer.writerows(data_rows)
browser,vendor,year_appeared
Chrome,Google,2008
Safari,Apple,2003
Edge,Microsoft,2015
Advanced CSV File Reading with DictReader
While each row in a CSV file can be treated as a list of values, they can also be converted into dictionaries, where the field names are the keys. This approach makes the data easier to read and understand. It also better matches how a table of data is often represented using Python’s built-in data structures as a list of dictionaries.
import csv
with open("some-other-file.csv", "r") as file:
reader = csv.DictReader(file)
for row in reader:
print(row)
browser,vendor,year_appeared
Chrome,Google,2008
Safari,Apple,2003
Edge,Microsoft,2015
{'browser': 'Chrome', 'vendor': 'Google', 'year_appeared': '2008'}
{'browser': 'Safari', 'vendor': 'Apple', 'year_appeared': '2003'}
{'browser': 'Edge', 'vendor': 'Microsoft', 'year_appeared': '2015'}
Advanced CSV File Writing with DictWriter
Just as reading a CSV file involves using a DictReader object, writing to a CSV file involves using a DictWriter object:
import csv
field_names = [
"browser",
"vendor",
"year_appeared"
]
data_rows = [
{
"browser": "Chrome",
"vendor": "Microsoft",
"year_appeared": 2008,
},
{
"browser": "Safari",
"vendor": "Apple",
"year_appeared": 2003,
},
{
"browser": "Edge",
"vendor": "Microsoft",
"year_appeared": 2015,
},
]
with open("yet-one-more-file.csv", 'w') as file:
writer = csv.DictWriter(file, fieldnames=field_names)
writer.writeheader()
for row in data_rows:
writer.writerow(row)