show 1.6.0

Debug Printing

Logging, assertions, unit tests, and interactive debuggers are all great tools. But sometimes you just need to print values as a program runs to see what’s going on. Every language has features to print text, but they’re rarely customized for printing debugging information. show is. It provides a simple, DRY mechanism to “show what’s going on.”

Sometimes programs print so that users can see things, and sometimes they print so that developers can. show() is for developers, helping rapidly print the current state of variables in ways that easily identify what value is being printed, without a lot of wasted effort. It replaces the craptastic repetitiveness of:

print "x: {0!r}".format(x)

with:

show(x)

And if you have a lot of output flowing by, and it’s hard to see your debugging output, try:

show(x, y, z, style='red')

And now you have debug output that clearly stands out from the rest.

But “debug printing is so very 1989!” you may say. “We now have logging, logging, embedded assertions, unit tests, …” Yes, that’s true. But wonderful as those things are, just showing your current program values is often what the doctor ordered.

And Much More

While avoiding a few extra characters of typing and a little extra program complexity is nice (very nice, actually), show does much more. As just a taste, show.changed() displays local values that have changed since it was last run:

def f():
    x = 4
    show.changed()
    x += 1
    retval = x * 3
    show.changed()
    return retval

When run will display:

x: 4
x: 5  retval: 15

Functions decorated with @show.inout show you input parameters as the function is called, then the return value later.:

@show.inout
def g(a):
    b = 3
    a += b
    show.changed()
    return a

g(4)

Displays:

g(a=4)
a: 7  b: 3
g(a=4) -> 7

(If you want this terser, decorate with @show.inout(only='out').)

If you run show.prettyprint() after importing, or alternatively if you import with from show.pretty import *, the Pygments syntax highlighter will (if installed), be used to colorize data values. This can significantly help see complex lists and dictionaries.

Finally, show does normal output too, just like say (with all of its high-level text formatting):

wizard = "Gandalf"
show("You have no power here, {wizard}!")

Prints:

You have no power here, Gandalf!

Long story short, show is a strong debugging companion that prints the maximum amount of useful information with the minimum amount of fuss.

For more, see the full documentation at Read the Docs.

New and Notable

Try from show.pretty import *.

IPython is now well-supported, either in a terminal window or a Jupyter Notebook. In other words, show now supports interactive usage. (The plain Python REPL is still only marginally supported, given significant weaknesses in its introspection support.)

A relatively new capability is to differentially set the formatting parameters on a method by method basis. For example, if you want to see separators in green and function call/return annotations in red:

show.sep.set(style='green')
show.inout.set(style='red')

You could long do this on a call-by-call basis, but being able to set the defaults just for specific methods allows you to get more formatting in with fewer characters typed. This capability is available on a limited basis: primarily for format-specific calls (blanklines, hr, sep, and title) and for one core inspection call (the inout decorator). It will be extended, and mapped back to underlying say and options features over time.