PYTHON ASSIGNMENT

Python Assignment

Python assignment

Introduction

The most basic activities of programmers are editing source code, running the program to test it, and debugging the program. (Python doesn't have a separate compilation phase.) A programming environment must of course support these activities. We have been developing a portable programming environment for Python named IDLE, which allows the user to execute individual statements interactively. It is mostly targeted at experienced programmers, but will server as a starting point for an environment for absolute beginners.

IDLE only scratches the surface of the kind of programming environment needed to help novice programmers. For example, its source code colorization and indentation features could be replaced by a much more powerful program checker which would point out all syntax errors, undefined identifiers, type mismatches, and so on, while the user is typing (like a spelling checker). The debugger could support retracing execution steps, editing the source code of the running program, etc. The program editor could support a flexible form of template-based editing (the Alice group has very good experiences with this in their limited domain). The undo feature, which currently allows undoing source code changes only, could be extended to undo changes to the run-time state of the program or even side-effects to the environment (within reason--we can't expect to undo printing or the sending of an email message). As an example, the Alice software provides full undo for all actions involving changes to the 3D world it manages.

"Undo" is an extremely important tool for beginners because it is the programmer's first line of defense. Along with version control, auto-save, and other features, the ability to rollback an unlimited number of near-term changes means that the programmer has more leeway to experiment and learn. However, most undo implementations are quite limited in their scope. Our approach will investigate such concepts as selective and global undo. In a traditional undo system, the editor simply keeps a linked list of changes to a file, and those changes can be unapplied or reapplied by moving through this list (there are variations on this theme, including undo rings, and undo/redo). One of the problems with traditional undo is where some undesirable changes overlap with some desirable changes; the programmer often has to lose the desirable ones to eliminate the undesirable ones.

With selective undo, changes can be localized to a finer granularity. For example, suppose a programmer made three changes to function A at the top of the file intermingled with four changes to function Z at the bottom of the file. Now the programmer discovers that function A should never have changed; selective undo allows changes to function A to be rolled back without affecting the changes to function Z.

Global undo is similar to what version control provides, where system level changes can be tagged and rolled back when they adversely affect the system. Where global undo differs however is that no a-priori decision has to be made about tagging.

We also plan to enhance the development environment with type-checking tools ...