Reading Files Python

This notebook will provide information regarding reading .txt files.

Table of Contents

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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 in Figure 1:

Figure 1: Labeled Syntax of a file object.

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 in figure 2:

Figure 2: The text file "Example1.txt".

First we load the file into the directory:

!wget -O /resources/data/Example1.txt https://s3-api.us-geo.objectstorage.softlayer.net/cf-courses-data/CognitiveClass/PY0101EN/labs/example1.txt

--2019-01-28 15:59:53--  https://s3-api.us-geo.objectstorage.softlayer.net/cf-courses-data/CognitiveClass/PY0101EN/labs/example1.txt
Resolving s3-api.us-geo.objectstorage.softlayer.net (s3-api.us-geo.objectstorage.softlayer.net)... 67.228.254.193
Connecting to s3-api.us-geo.objectstorage.softlayer.net (s3-api.us-geo.objectstorage.softlayer.net)|67.228.254.193|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 45 [text/plain]
Saving to: ‘/resources/data/Example1.txt’

/resources/data/Exa 100%[=====================>]      45  --.-KB/s   in 0s     

2019-01-28 15:59:53 (28.5 MB/s) - ‘/resources/data/Example1.txt’ saved [45/45]

We read the file:

example1="/resources/data/Example1.txt"
file1 = open(example1,"r")

We can view the attributes of the file.

The name of the file:

file1.name

'/resources/data/Example1.txt'

The mode the file object is in:

file1.mode

'r'

We can read the file and assign it to a variable :

FileContent=file1.read()
FileContent

'This is line 1 \nThis is line 2\nThis is line 3'

The “/n” tells python that there is a new line.

We can print the file:

print(FileContent)

This is line 1 
This is line 2
This is line 3

The file is of type string:

type(FileContent)

str

We must close the file object:

file1.close()

file1

<_io.TextIOWrapper name='/resources/data/Example1.txt' mode='r' encoding='UTF-8'>

A Better Way to Open a File

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.

with open(example1,"r") as file1:
    FileContent=file1.read()
    print(FileContent)

This is line 1 
This is line 2
This is line 3

The file object is closed, you can verify it by running the following cell:

file1.closed

True

We can see the info in the 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 summarise the steps in a figure:

The syntax for opening a file using a 'with' statement.

with open(example1,"r") as file1:
    FileContent=file1.readlines()
    print(FileContent)

['This is line 1 \n', 'This is line 2\n', 'This is line 3']

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():

with open(example1,"r") as file1:
    print(file1.read(4))

This

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() **:

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 colour represents the part of the file read after the method read() is called:

Illustration using the method .read() to call different characters

Here is an example using different values:

with open(example1,"r") as file1:
    print(file1.read(16))
    print(file1.read(5))
    print(file1.read(9))

This is line 1 

This 
is line 2

We can also read one line of the file at a time using the method readline():

 with open(example1,"r") as file1:
    print("first line: " + file1.readline())

first line: This is line 1 

We can use a loop to iterate through each line:

 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

We can use the method readline() to save the text file to a list:

with open(example1,"r") as file1:
    FileasList=file1.readlines()

Each element of the list corresponds to a line of text:

FileasList[0]

'This is line 1 \n'

FileasList[1]

'This is line 2\n'

FileasList[2]

'This is line 3'

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### About the Author: [Joseph Santarcangelo]( https://www.linkedin.com/in/joseph-s-50398b136/) has a PhD in Electrical Engineering, his research focused on using machine learning, signal processing, and computer vision to determine how videos impact human cognition. Joseph has been working for IBM since he completed his PhD.

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Copyright © 2017 [cognitiveclass.ai](cognitiveclass.ai?utm_source=bducopyrightlink&utm_medium=dswb&utm_campaign=bdu). This notebook and its source code are released under the terms of the [MIT License](https://bigdatauniversity.com/mit-license/).​