Encapsulate usage of colorama within ansi.py

[tleonhardt]

Now that all of the ANSI color code stuff has been encapsulated within the ansi.py module, it would be possible to completely remove the dependency on colorama.

If we did this, we could still easily support ANSI escapes codes on Windows 10, macOS, and Linux but would likely lose support for Windows 7 which we probably don't want to do at this time.

However, in order to move in the direction of making it easy to remove the dependency on colorama in the future, it would be desirable to limit its usage to a single place - ansi.py.

[tleonhardt]

How and where does cmd2 use colorama

Here is a quick survey of where cmd2 uses colorama and what it uses from it

cmd2.py

• colorama.init(strip=False)
  • On Windows, calling init() will filter ANSI escape sequences out of any text sent to stdout or stderr, and replace them with equivalent Win32 calls. The magic provided by this function on Windows would be my biggest concern in removing colorama. However, I suspect that in newer versions of Windows terminals, ANSI escape codes will "just work".
• colorama.Cursor.DOWN() and colorama.Cursor.UP()
  • Cursor relative vertical positioning one line down or up, respectively
• colorama.ansi.clear_line()
  • Clears the current line
• colorama.ansi.set_title()
  • Sets the windows title

ansi.py

• colorama.Fore, colorama.Back, colorama.Style
  • ANSI escape codes for foreground and background color as well as styles/effects
• colorama.ansi.code_to_chars()
  • Convert ANSI numbers to escape sequences for underline on/off formatting

[tleonhardt]

Replacing all of the above uses of colorama with custom code which works on Linux and macOS should be relatively easy.

However, replacing all of that with custom code which works reliably on Windows, macOS, and Linux might be challenging unless we only want to support bleeding edge Windows terminals.

My opinion (weakly held) is that we should close this for now and revisit this in a year or so once Windows terminals with ANSI support have become much more common.

What do other people think?

[tleonhardt]

One thing we could do to make it easier to remove or replace the usage of colorama would be to encapsulate all usages of it within ansi.py where we define functions in ansi.py which at first are simple wrappers around the equivalent colorama functions, but at a later date could be replaced with custom code.

We could also remove reliance on constants from colorama with our own constants.