1. CSV files
Professor Hugh C. Lauer CS-1004 — Introduction to Programming for Non-Majors
(Slides include materials from Python Programming: An Introduction to Computer Science, 2nd edition, by John Zelle and copyright notes by Prof. George Heineman of Worcester Polytechnic Institute)
CS-1004, A-Term 2014
CSV files

2. Introduction to CSV files
“CSV” — Comma Separated Values
Common format for interchange among spreadsheets
One “Header” row
Many “rows” of data
Each row is called a “record”
Record:–
String containing “fields” separated by commas
Each field is a substring of text
“Meanings” of fields
Defined by Header Row
CS-1004, A-Term 2014
CSV files

3. Example Header Row:– Data (subsequent rows)
LastName,FirstName,Initial,Course,Time
Data (subsequent rows)
Lauer,Hugh,C,CS-1004,0800 Wills,Craig,E,CS-3013,1200 Hamel,Glynis,M,CS-1101,1000 Rich,Charles,,CS-1102,1000
Easily import to / exported from spreadsheet
Each “row” of csv-file is row of spreadsheet
Commas delineate columns
Header row indicates meanings of columns
CS-1004, A-Term 2014
CSV files

4. Processing CSV files in Python
Module “csv”
Methods
csv.reader() — returns a “reader” object
csv.writer() — returns a “writer” object
csv.DictReader() — returns a “reader” object that makes each row a mini dictionary
csv.DictWriter() — returns a “writer” object that constructs output from mini dictionary …
Other methods
Limit field sizes
Manage “dialects” of csv files
“Sniff” out the format of a csv file
CS-1004, A-Term 2014
CSV files

5. CSV Reader Acts somewhat like file.read()
for row in reader: #process row list.append(row)
Format of each row:–
List of strings
Each element of list represents one field
Empty fields from csv file  null strings in list
Numbers not by default interpreted!
Settable option
Example
smallDataSet.csv
CS-1004, A-Term 2014
CSV files

6. CSV DictReader Each row is actually a mini-dictionary
Key names taken from header row
By default!
Controllable
Key names of all rows are same
Enables access to fields by name
Without having to count fields in rows
Combining multiple data sets with different formats
E.g., two data sets may both have 'latitude' and 'longitude' fields but differ in all other respects
CS-1004, A-Term 2014
CSV files

7. Questions?
CS-1004, A-Term 2014
CSV files

8. Homework #6 Plotting civic data on a map Two data sets
Crime records in Sacramento, CA for January 2006
Real estate transactions in Sacramento region for one week in May 2008
Both as CSV files
Each record includes latitude and longitude
Draw colored circles on map of region
Using graphics package from textbook
graphics.Image() object
CS-1004, A-Term 2014
CSV files

9. Apologia Homework assignment not yet on course web site
As soon as possible
Due Monday, October 13
CS-1004, A-Term 2014
CSV files

10. Questions?
CS-1004, A-Term 2014
CSV files