Behind the Scenes: How Python Works

Whether you are running Python code as a script or interactively in a shell, the Python interpreter does a great deal of work to carry out the instructions in your program. This work can be broken into a series of steps, as shown in Figure.

1 The interpreter reads a Python expression or statement, also called the source code, and verifies that it is well formed. In this step, the inter-preter behaves like a strict English teacher who rejects any sentence that

does not adhere to the grammar rules, or syntax,of the language. As soon as the interpreter encounters such an error, it halts translation with an error message.

2. If a Python expression is well formed, the interpreter then translates it to an equivalent form in a low-level language called byte code. When the interpreter runs a script, it completely translates it to byte code.

3. This byte code is next sent to another software component, called the Python virtual machine (PVM), where it is executed. If another error occurs during this step, execution also halts with an error message.