23 
'Hello ' + ('there' if name is None else name)

Is the equivalent of 

msg = 'Hello ' if name is None: msg += 'there' else: msg += name

What is the equivalent of this:

msg = 'Hello ' if name is None: msg += 'there' elif name == 'Mr Anderson' msg += 'Neo' else: msg += name

EDIT: for reference here is the code I wanted to shrink

srepr = '\'Modify ' if self.register == 'p': srepr += 'Pointer' elif self.register == 'v': srepr += 'Value' else srepr += 'Unknown' srepr += ' By ' + str(self.delta) + '\''
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  • 4
    srepr+={'p': 'Pointer', 'v': 'Value'}.get(self.register,'Unknown') Commented Jan 6, 2011 at 13:42

7 Answers 7

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38 
msg = "Hi " + ("there" if not name else ("Neo" if name == "Anderson" else name))

I think that's pretty unreadable, though.

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3 Comments

You have unnecessary parentheses which make this less readable. See my answer for a clearer solution.
@glenn. I added those parentheses in order to make it more readable, but I guess that's subjective. In any case I think we all agree nobody should ever write nothing similar.
Nice answer - but if I ever see this in a production codebase, I'm going to have a long day. :P
8

Use a dictionary to perform a mapping:

srepr = "'Modify " + {"p": "Pointer", "v": "value"}.get(self.register, "Unknown")

(by the way, instead of '\'...' you can use "'... for a bit more clarity.

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8 
msg = 'Hello ' + ( 'there' if name is None else 'Neo' if name == 'Mr Anderson' else name )

This is a reiteration of several other answers, but with nicer formatting. I consider this most readable, and this is the approach I would use.

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3 
'Hello ' + \ ('there' if name is None else \ 'Neo' if name == 'Mr Anderson' else \ name)

I recommend against this; if your conditions become this complex, stick it in a function.

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1 Comment

This is the approach I would use, but as it's written here, the formatting is unnecessarily noisy. See my answer for a version without backslashes and with consistent indentation.
2

Do not do it.

Do this instead:

% python -m this | sed 's/^R.*/======>&<======/'

EDIT: For reference, here is how I would refactor this code...

Whenever I see elif, I think dict.

#!/usr/bin/env python class Shrink(object): types = { 'p': 'Pointer', 'v': 'Value', } def shrink_this(self): return "'Modify %s By %s'" % ( self.types.get(self.register, 'Unknown'), self.delta) import unittest class TestShrink(unittest.TestCase): def test_p(self): s = Shrink(); s.register = 'p' s.delta = 'delta' self.assertEquals("'Modify Pointer By delta'", s.shrink_this()) def test_u(self): s = Shrink(); s.register = 'u' s.delta = 'echo' self.assertEquals("'Modify Unknown By echo'", s.shrink_this()) def test_v(self): s = Shrink(); s.register = 'v' s.delta = 'foxtrot' self.assertEquals("'Modify Value By foxtrot'", s.shrink_this()) if __name__ == '__main__': unittest.main()

Were you to need to add r for reference or pp for pointer-to-pointer, only types requires a change and your code remains readable.

Readability counts.

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3 Comments

Ouch. Why the down-vote? "The Zen of Python" is important reading for any Python programmer (along with PEP008). The sed command emphasises the point.
The question says Python 3.x. Use return "'Modify {} By {}'".format( self.types.get(self.register, 'Unknown'), self.delta)
And a second down-vote: "If you see misinformation, vote it down. Add comments indicating what, specifically, is wrong. Provide better answers of your own. Best of all — edit and improve the existing questions and answers!" --Be Honest, SO FAQ <stackoverflow.com/faq>
0

You could also do this:

msg= 'Hello ' + {name is None: 'there', name == 'Mr Anderson': 'Neo'}.get(True, name)

So either of name is None or name == 'Mr Anderson' is True, or none of them is True, then name will be used.

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-2

Firstly, run 'pip install pyswitch'

Then:

import pyswitch mySwitch = pyswitch.Switch() @mySwitch.case(None): def gotNone(value): return 'Hello there' @mySwitch.case('Mr. Anderson') def gotMrAnderson(value): return 'Hello Neo' @mySwitch.default def gotDefault(value): return 'Hello %s' % value msg = mySwitch.switch(None) # Returns 'Hello there' msg = mySwitch.switch('Mr. Anderson') # Returns 'Hello Neo' msg = mySwitch.switch('OoglyMoogly') # Returns 'Hello OoglyMoogly'
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As the length of your 'elif' chain grows, this solution's appeal grows. It's basically a something like a C language switch statement for Python. See pypi.python.org/…
if it comes to that, one could just use a dictionary with cases as keys, and a possibly lambda function as values. way much simpler that a pyswitch even in large statments.