14.1 Reading from files

Learning objectives

By the end of this section you should be able to

Understand how to open a file using the open function.
Demonstrate how to read information from a file using read, readline, and readlines.

Opening a file

Reading information from and writing information to files is a common task in programming.

Python supports the opening of a file using the open function.

Using `read` and reading lines

Python provides functions that can be called on a file object for reading the contents of a file:

The read function reads the contents of a file and returns a string.
The readline function reads the next line in a file and returns a string.
The readlines function reads the individual lines of a file and returns a string list containing all the lines of the file in order.

Example 1 Using read and readlines

A file called input.txt has the following contents:

"""Demonstrating read() and readlines()"""

# Using read()
# Open the file and associate with a file object
infile = open("input.txt")

# Read the contents of the file into a string
str1 = infile.read()

# Print str1
print("Result of using read():")
print(str1)

# Always close the file once done using the file
infile.close()

# Using read()
# Open the file and associate with a file object
infile2 = open("input.txt")

# Read the contents of the file into a string list
str_list = infile2.readlines()

# Printing the third item in the string list.
print("Result of using readlines() and printing the third item in the string list:")
print(str_list[2])

# Always close the file once done using the file
infile2.close()

The code's output is:


    Result of using read():
    12
    55
    5
    91
    Result of using readlines() printing the third item in the string list:
    5

Note

Reading files

Suppose fileobj = open("input.txt") has already been executed for each question below.

input.txt:


    Hello world!
    How are you?

Note

Reading from a file

Open the file test.txt and print the file's contents.

Note

Reading from a file line by line

The file input.txt is shown. The file represents a set of integers. Line 1 of the file specifies how many integers follow. Write a program that reads from this file and determines the average of the numbers following the first line.

input.txt

14.1 Reading from files

Learning objectives

Opening a file

Using read and reading lines

Using `read` and reading lines