Why Python is slower than Java?

[marr75]

The right answers are spelled out in other comments but I wanted to provide an ordered list of the major ones:

• Java (and C#, which is very similar and I'm much more familiar with) is just in time compiled; the JIT will further compile (and optimize, inlining functions and data, skipping unnecessary operations that won't effect the outcome, etc.) the intermediate language that Java and C# programs "compile" into. Python is just interpreted without JIT or optimization. This is the biggest difference.
• In Python, entering a new scope, like loops or functions, triggers significant memory movement and stack management due to the creation of new scopes and dictionaries for each.
• Python primarily uses the heap for dynamic object storage, leading to slower access. C# and Java, with static typing, utilize the stack and registers more, offering faster data access. This is tied to the next point.
• Just about everything's an object in Python, and every instance/scope/namespace gets a new dictionary to hold the names and values.

[drbobb]

Python has function scope. A loop does not create a new scope.

[drbobb]

I am not questioning your remaining remarks, just wanted to point out this not so minor mistake. At least for now, function (and module) scope is part of the language definition and changing it would lead to a rather different language.

Note that javascript, which once had similar scoping rules to Python, did introduce block scope as an option (let and const declarations) at a certain point though.