Mac Attack

a if test else b

x << yReturns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.

x >> yReturns x with the bits shifted to the right by y places. This is the same as //'ing x by 2**y.

x & yDoes a "bitwise and". Each bit of the output is 1 if the corresponding bit of x AND of y is 1, otherwise it's 0.

Re: Python : map and filter vs for loops The underlying implementation of map and filter are different than loops, even though they accomplish the same thing. Which idiom runs fastest can change from version to version. Right now I think list comprehensions are the fastest. So instead of Code: filter(f, range(2,25)), the list comprehension would be Code: [x for x in range(2,25) if f(x)] and instead of Code: map(cube, range(1, 11)) the list comprehension would be Code: [cube(x) for x in range(1,11)]

which is just ugly. .format doesn't have those issues. Also in the second example you gave, the .format example is much cleaner looking.

Unicode and new style string formatting Python 2.6 and Python 3 gain a new style of string formatting, which is apparently based on the string formatting in C#. I wasn't a big fan of the string formatting in C# and so wasn't very excited about it moving into Python, but as is to be expected it has grown a bit on me.

As always, the best solution is to not mix Unicode and byte-strings but to keep all strings in Unicode and only perform the encode when actually needed.

So why does this behaviour matter? Well it particularly matters for framework authors formatting messages based on 'user' input. This is the case with unittest, which creates error messages when tests fail. The error messages internally in unittest are byte-strings and they are often mixed with user supplied messages using string formatting. We use old-style (% based) formatting, so if the user supplies byte-strings then the resulting messages will be byte-strings. If the user supplies Unicode strings then the resulting messages will be in Unicode. Because all the internal unittest messages are ascii only we can guarantee than an implicit decode to Unicode will succeed - so the user can choose the output type by varying the type of the messages they provide.

"""''.format_map() in Python 2.x"""

No need to jump through these loops, See 5.1.1 Using Lists as Stacks

If print() is a function, it would be much easier to replace it within one module (just def print(*args):...) or even throughout a program (e.g. by putting a different function in __builtin__.print). As it is, one can do this by writing a class with a write() method and assigning that to sys.stdout -- that's not bad, but definitely a much larger conceptual leap, and it works at a different level than print.