Table of Contents
Reading Text Files
One way to read or write a file in Python is to use the built-in open
function. The open
function provides a File object that contains the methods and attributes you need in order to read, save, and manipulate the file. In this notebook, we will only cover .txt files. The first parameter you need is the file path and the file name. An example is shown as follow:
The mode argument is optional and the default value is r. In this notebook we only cover two modes:
- r Read mode for reading files
- w Write mode for writing files
For the next example, we will use the text file Example1.txt. The file is shown as follow:
We read the file:
# Read the Example1.txt
example1 = "Example1.txt"
file1 = open(example1, "r")
We can view the attributes of the file.
File name
The name of the file:
'Example1.txt'
Mode of file object
The mode the file object is in:
# Print the mode of file, either 'r' or 'w'
file1.mode
'r'
Read the file
We can read the file and assign it to a variable :
# Read the file
FileContent = file1.read()
FileContent
'This is line 1\nThis is line 2\nThis is line 3'
The /n means that there is a new line.
Print the file
We can print the file:
# Print the file with '\n' as a new line
print(FileContent)
This is line 1 This is line 2 This is line 3
Type of file content
The file is of type string:
# Type of file content
type(FileContent)
str
Close file object
We must close the file object:
# Close file after finish
file1.close()
A Better Way to Open a File
Using ‘with’ statement
Using the with
statement is better practice, it automatically closes the file even if the code encounters an exception. The code will run everything in the indent block then close the file object.
# Open file using with
with open(example1, "r") as file1:
FileContent = file1.read()
print(FileContent)
This is line 1 This is line 2 This is line 3
Verify if the file is closed
The file object is closed, you can verify it by running the following cell:
# Verify if the file is closed
file1.closed
True
See file content
We can see the info in the file:
# See the content of file
print(FileContent)
This is line 1 This is line 2 This is line 3
The syntax is a little confusing as the file object is after the as
statement. We also don’t explicitly close the file. Therefore we summarize the steps in a figure:
Read first x characters
We don’t have to read the entire file, for example, we can read the first 4 characters by entering three as a parameter to the method .read():
# Read first four characters
with open(example1, "r") as file1:
print(file1.read(4))
This
Read certain amount of characters
Once the method .read(4)
is called the first 4 characters are called. If we call the method again, the next 4 characters are called. The output for the following cell will demonstrate the process for different inputs to the method read()
:
# Read certain amount of characters
with open(example1, "r") as file1:
print(file1.read(4))
print(file1.read(4))
print(file1.read(7))
print(file1.read(15))
This is line 1 This is line 2
The process is illustrated in the below figure, and each color represents the part of the file read after the method read()
is called:
# Read certain amount of characters
with open(example1, "r") as file1:
print(file1.read(16))
print(file1.read(5))
print(file1.read(9))
This is line 1 T his i s line 2
Read line
We can also read one line of the file at a time using the method readline()
:
# Read one line
with open(example1, "r") as file1:
print("first line: " + file1.readline())
first line: This is line 1
Iterate through the lines
We can use a loop to iterate through each line:
# Iterate through the lines
with open(example1,"r") as file1:
i = 0;
for line in file1:
print("Iteration", str(i), ": ", line)
i = i + 1;
Iteration 0 : This is line 1 Iteration 1 : This is line 2 Iteration 2 : This is line 3
Save as a list
We can use the method readlines()
to save the text file to a list:
# Read all lines and save as a list
with open(example1, "r") as file1:
FileasList = file1.readlines()
Each element of the list corresponds to a line of text:
# Print the first line
FileasList[0]
'This is line 1\n'
# Print the second line
FileasList[1]
'This is line 2\n'
# Print the third line
FileasList[2]
'This is line 3'