How (Not) to Obfuscate Your Python Code

The fact that the body of a lambda has to be a single expression (not a series of statements) would seem to place severe limits on how much logic you can pack into a lambda. If you know what you’re doing, though, you can code most statements in Python as expression-based equivalents.

For example, if you want to print from the body of a lambda function, simply say sys.stdout.write(str(x)+'\n'), instead of print(x) (recall from Chapter 11 that this is what print really does). Similarly, to nest logic in a lambda, you can use the if/else ternary expression introduced in Chapter 12, or the equivalent but trickier and/or combination also described there. As you learned earlier, the following statement:

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if a:
    b
else:
    c

can be emulated by either of these roughly equivalent expressions:

b if a else c
((a and b) or c)

Because expressions like these can be placed inside a lambda, they may be used to implement selection logic within a lambda function:

>>> lower = (lambda x, y: x if x < y else y)
>>> lower('bb', 'aa')
'aa'
>>> lower('aa', 'bb')
'aa'

Furthermore, if you need to perform loops within a lambda, you can also embed things like map calls and list comprehension expressions (tools we met in earlier chapters and will revisit in this and the next chapter):

>>> import sys
>>> showall = lambda x: list(map(sys.stdout.write, x))        # Use list in 3.0

>>> t = showall(['spam\n', 'toast\n', 'eggs\n'])
spam
toast
eggs

>>> showall = lambda x: [sys.stdout.write(line) for line in x]

>>> t = showall(('bright\n', 'side\n', 'of\n', 'life\n'))
bright
side
of
life

Now that I’ve shown you these tricks, I am required by law to ask you to please only use them as a last resort. Without due care, they can lead to unreadable (a.k.a. obfuscated) Python code. In general, simple is better than complex, explicit is better than implicit, and full statements are better than arcane expressions. That’s why lambda is limited to expressions. If you have larger logic to code, use def; lambda is for small pieces of inline code. On the other hand, you may find these techniques useful in moderation.