physical lines & logical lines

In Python, understanding the difference between physical lines and logical lines is crucial for comprehending the structure of a program.

Physical Lines

Physical lines refer to the lines you actually see in your text editor. Each of these lines is terminated by a newline character. In other words, every time you hit “Enter” in your code editor, you create a new physical line. For example:

a = 5
b = 6

In this simple example, there are two physical lines: a = 5 and b = 6.

Logical Lines

Logical lines refer to the lines that the Python interpreter uses to understand the logic of your code. Generally, one logical line corresponds to one Python statement, meaning it represents one complete operation or command. Most of the time, one logical line maps to one physical line, but that’s not always the case.

In some situations, one logical line may consist of multiple physical lines. For instance, when you have parentheses (either round brackets, square brackets, or curly braces) in your code:

a = [
    1, 2, 3,
    4, 5, 6
]

Here, although there are multiple physical lines, they together form a single logical line.

Another case is when a backslash (\) is used to indicate that a logical line should continue onto the next physical line:

s = "This is a string " \
    "that continues onto the next line."

In this instance, there are two physical lines, but they merge to form one logical line due to the use of the backslash.

In summary, physical lines are the actual lines in your source code, while logical lines are the complete statements that the Python interpreter executes. Logical lines can be made up of one or multiple physical lines, depending on the structure of your code.