How to Read a Portion of a File in Python

Summary: in this tutorial, you lot learn diverse ways to read text files in Python.

TL;DR

The post-obit shows how to read all texts from the readme.txt file into a cord:

            
                              with                open up('readme.txt')                as                f:     lines = f.readlines()            
                          Code language:              JavaScript              (              javascript              )                      

Steps for reading a text file in Python

To read a text file in Python, yous follow these steps:

• First, open a text file for reading past using the open up() office.
• Second, read text from the text file using the file read(), readline(), or readlines() method of the file object.
• Tertiary, close the file using the file shut() method.

1) open() part

The open() part has many parameters but you'll be focusing on the kickoff ii.

            
              open(path_to_file, mode)            
          

The path_to_file parameter specifies the path to the text file.

If the file is in the aforementioned binder as the program, yous only need to specify the name of the file. Otherwise, you need to specify the path to the file.

To specify the path to the file, you utilise the forward-slash ('/') fifty-fifty if you're working in Windows.

For example, if the file is readme.txt stored in the sample folder as the programme, yous need to specify the path to the file every bit c:/sample/readme.txt

The mode is an optional parameter. Information technology's a string that specifies the fashion in which you want to open up the file.

The post-obit table shows available modes for opening a text file:

Mode	Description
'r'	Open up for text file for reading text
'due west'	Open a text file for writing text
'a'	Open a text file for appending text

For example, to open a file whose name is the-zen-of-python.txt stored in the same folder equally the programme, you use the following lawmaking:

            
                              f = open up('the-zen-of-python.txt','r')            
                          Code linguistic communication:              JavaScript              (              javascript              )                      

The open up() part returns a file object which you will use to read text from a text file.

ii) Reading text methods

The file object provides y'all with three methods for reading text from a text file:

• read() – read all text from a file into a cord. This method is useful if you have a small file and you want to dispense the whole text of that file.
• readline() – read the text file line by line and return all the lines as strings.
• readlines() – read all the lines of the text file and render them as a listing of strings.

3) close() method

The file that y'all open up volition remain open until you lot shut it using the close() method.

Information technology'southward of import to shut the file that is no longer in employ. If you don't close the file, the program may crash or the file would be corrupted.

The following shows how to call the close() method to shut the file:

            
                              f                .close()            
                          Code language:              CSS              (              css              )                      

To close the file automatically without calling the close() method, you use the with statement like this:

            
                              with                open up(path_to_file)                as                f:     contents = f.readlines()            
                          Code language:              JavaScript              (              javascript              )                      

In practice, you'll employ the with argument to close the file automatically.

Reading a text file examples

We'll use the-zen-of-python.txt file for the demonstration.

The following example illustrates how to employ the read() method to read all the contents of the the-zen-of-python.txt file into a string:

            
                              with                open up('the-zen-of-python.txt')                as                f:     contents = f.read()     print(contents)            
                          Code language:              JavaScript              (              javascript              )                      

Output:

            
              Cute is better than ugly. Explicit is better than implicit. Simple is better than complex. ...                          
          

The following case uses the readlines() method to read the text file and returns the file contents as a list of strings:

            
              lines = []                with                open('the-zen-of-python.txt')                equally                f:     lines = f.readlines()  count =                0                for                line                in                lines:     count +=                1                print(f'line {count}: {line}')                          
                          Code linguistic communication:              JavaScript              (              javascript              )                      

Output:

            
              line one: Cute is better than ugly.  line 2: Explicit is ameliorate than implicit.  line three: Simple is better than complex. ...                          
          

The post-obit case shows how to utilize the readline() to read the text file line past line:

            
                              with                open('the-zen-of-python.txt')                as                f:     line = f.readline()                while                line:         line = f.readline()         print(line)            
                          Code language:              JavaScript              (              javascript              )                      

Output:

            
              Explicit is improve than implicit.  Simple is better than complex.  Complex is meliorate than complicated. ...                          
          

A more curtailed style to read a text file line past line

The open() role returns a file object which is an iterable object. Therefore, yous can employ a for loop to iterate over the lines of a text file as follows:

            
                              with                open('the-zen-of-python.txt')                as                f:                for                line                in                f:         impress(line)            
                          Code language:              JavaScript              (              javascript              )                      

This is more concise way to read a text file line by line.

Read UTF-8 text files

The code in the previous examples works fine with ASCII text files. However, if you're dealing with other languages such as Japanese, Chinese, and Korean, the text file is not a uncomplicated ASCII text file. And information technology'due south likely a UTF-8 file that uses more than than just the standard ASCII text characters.

To open a UTF-8 text file, you demand to pass the encoding='utf-8' to the open up() function to instruct it to expect UTF-8 characters from the file.

For the demonstration, you'll use the following quotes.txt file that contains some quotes in Japanese.

The following shows how to loop through the quotes.txt file:

            
                              with                open('quotes.txt', encoding='utf8')                as                f:                for                line                in                f:         print(line.strip())                          
                          Code linguistic communication:              JavaScript              (              javascript              )                      

Output:

Summary

• Use the open() function with the 'r' mode to open a text file for reading.
• Utilize the read(), readline(), or readlines() method to read a text file.
• E'er close a file after completing reading it using the close() method or the with argument.
• Utilize the encoding='utf-8' to read the UTF-8 text file.

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Source: https://www.pythontutorial.net/python-basics/python-read-text-file/

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