Unit 5-

Lesson 2-Reading Records

PART 1- Records in Files

In this lesson we learn how to read data from a file when it is stored as a collection of data called a record. Depending on how the data is stored we have different strategies for processing the data.

____________________

Lesson2-1-Records

PART 2 - Process Records

records.text contains a number of records which need to read, printed out in a table, with summary data extracted from the temperature and the population fields. Complete the 3 steps in the program so that the output looks like the following. Be sure to use formatting so he table is neatly aligned.

File Operations

f = open(filename, mode)

Opens the file specified by the string filename. The mode parameter indicates whether the file is opened for reading ("r") or writing ("w"). A file object is returned.

f.close()

Closes a previously opened file. Once closed, the file cannot be used until it has been reopened.

string = f.readline()

Reads the next line of text from an input file and returns it as a string. An empty string "" is returned when the end of file is reached.

string = f.read(num)

string = f.read()

Reads the next num characters from the input file and returns them as a string. An empty string is returned when all characters have been read from the file. If no argument is supplied, the entire contents of the file is read and returned in a single string.

f.write(string)

Writes the string to a file opened for writing.

PART 3- CSV Files Format

To process data from spreadsheets we can use a common intermediate format called Comma Separated Values (CSV), which is a so common that python has specific support for this data format.

____________________

Lesson2-2-CSVFiles

PART 4 - Process CSV Files

The movies.csv file contains data on thousands of movies with the following 5 fields in CSV format per movie.

"Name","Year","Directors","Producers","Actors"

Complete the program so that it reads the movies.csv file, filters the data for movies made between 1990 and 1999 (inclusive) and creates a new CSV file with just the following 3 fields,

"Name","Year","Actors"

Second Challenge: Modify the code so that you also filter movies which contain a specific actor name.

PART 5- A Process for processing text files

To process data from a file you have to make a series of decisions based on the file data format. In this example we walk through and example, and show the code in Part 6 of this lesson.

____________________

Lesson2-3-Approaches to file processing

PART 6 - Example - Calculating World Population Density

Run the program below to see the how it creates a new file called world_pop_densit.txt which is done by combining data from the two input files as described in the slides above.

Page updated

Report abuse