With Statement in Python (35/100 Days of Python)

Day 35 of the “100 Days of Python” blog post series covering the with statement

The with statement in Python is used to work with resources that need to be properly managed, such as files, sockets, and databases. The with statement provides a convenient way to ensure that resources are properly acquired and released, even in the case of exceptions.

The Basic Syntax of the with Statement

The basic syntax of the with statement includes the with keyword followed by an expression and then as and a variable:

with expression [as variable]:
    ...

The expression is an object that is being managed, such as a file or a database connection. The variable is an optional identifier that can be used to refer to the object within the with block.

Reading From a File Using the With Statement

One common use case for the with statement is reading a file. With the with statement, you can ensure that the file is properly closed, even if an exception occurs while reading the file:

with open('example.txt', 'r') as f:
    contents = f.read()
    # Do something with the contents of the file

In this example, the file example.txt is opened using the open function, and a reference to the file object is stored in the variable f. Within the with block, the contents of the file are read using the read method and stored in the variable contents. When the with block is exited, the file is automatically closed, even if an exception occurs.

Writing to a File Using the With Statement

The with statement can also be used when writing to a file:

with open('example.txt', 'w') as f:
    f.write('Hello, World!')

In this example, the file example.txt is opened using the open function in write mode, and a reference to the file object is stored in the variable f. Within the with block, the string "Hello, World!" is written to the file using the write method. When the with block is exited, the file is automatically closed, even if an exception occurs.

The with statement in Python is a convenient way to manage resources that need to be properly acquired and released, such as files, sockets, and databases (which we will discuss later in the series). With the with statement, you can ensure that resources are properly closed, even if an exception occurs, and avoid potential bugs related to resource management. Whether you are reading from or writing to a file, the with statement can help you write cleaner and more robust code.

Working With Multiple Files

When working with multiple files, the with statement can be used to manage each file separately, making it easier to handle errors and exceptions that may occur.

Let’s consider a real-world scenario where we need to read data from two different files and write the combined data to a third file. In this scenario, the with statement can be used to manage each of the files, as shown below:

with open('names.txt', 'r') as name_file, open('surnames.txt', 'r') as surname_file:
    names = name_file.read()
    surnames = surname_file.read()

with open('full-names.txt', 'w') as f:
    for name, surname in zip(names, surnames):
        f.write(f'{name} {surname}\n')

In this example, the first with statement opens two files, names.txtand surnames.txt, in read mode ('r') and stores references to the file objects in the variables name_file and surname_file, respectively. Within the with block, the contents of both files are read and stored in the variables names and surnames.

When the with block is exited, both the names.txt and surnames.txt files are automatically closed, even if an exception occurs while reading the data.

The second with statement opens a file full-names.txt in write mode ('w') and stores a reference to the file object in the variable f. Within the with block, the contents of names and surnames are written to the full-names.txt file using the write method line-by-line.

Similarly, when the second with block is exited, the full-names.txt file is automatically closed.

With Statements Enclosed in Parentheses

Starting from the 3.10 version, Python allows using enclose the with statements in parentheses: reference.

This means that we can have multiple context managers on different lines as easily as:

with (open('first.txt', 'r') as f1):
    ...

with (
    open('second', 'r'),
    open('third', 'w'),
):
    ...

with (open('one.txt') as one,
      open('two.txt')):
    ...

with (
    open('three.txt', 'w') as three,
    open('four.txt', 'r') as four
):
    ...

This is especially useful when working with many files at the same time.

with statements are actually more powerful and provide flexibility to work with much more than only files. We’ll touch on those topics and how they can be used with databases or sockets in the coming series.

What’s next?

• If you found this story valuable, please consider clapping multiple times (this really helps a lot!)
• Hands-on Practice: Free Python Course — with statement in Python
• Full series: 100 Days of Python
• Previous topic: Working With Files
• Next topic: Automating Data Cleaning With Python