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Benjamin Bandt-Horn

Great Python Tricks for avoiding unnecessary loops in your code - Udacity Forums - 0 views

forums.udacity.com/...unnecessary-loops-in-your-code

python tricks loops List Comprehensions

shared by Benjamin Bandt-Horn on 30 Dec 13 - No Cached
  • To do element-wise operations on a list - for example, to produce a list consisting of each element of list A multiplied by 2 Method 1 [2*x for x in A] - this technique is called list comprehension Method 2 if you have defined a function double(x) which doubles x map(double, A) Method 3 define the function that doubles x on the fly, anonymously map(lambda x: 2*x, A)
  • Benjamin Bandt-Horn on 30 Dec 13
     
    To do element-wise operations on a list - for example, to produce a list consisting of each element of list A multiplied by 2 Method 1 [2*x for x in A] - this technique is called list comprehension Method 2 if you have defined a function double(x) which doubles x map(double, A) Method 3 define the function that doubles x on the fly, anonymously map(lambda x: 2*x, A)
Benjamin Bandt-Horn

Python : map and filter vs for loops - 0 views

ubuntuforums.org/showthread.php

python map filter loops List Comprehensions

shared by Benjamin Bandt-Horn on 14 Dec 13 - No Cached
  • 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)]
  • Benjamin Bandt-Horn on 14 Dec 13
     
    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.
Benjamin Bandt-Horn

Map. - 0 views

docs.python.org/...node81.html

python map List Comprehensions

shared by Benjamin Bandt-Horn on 14 Dec 13 - No Cached
  • Benjamin Bandt-Horn on 14 Dec 13
     
    Combining these two special cases, we see that map(None, list1, list2) is a convenient way of turning a pair of lists into a list of pairs. For example:         >>> seq = range(8)        >>> map(None, seq, map(lambda x: x*x, seq))        [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49)]        >>>
Benjamin Bandt-Horn

Classes & Iterators - Dive Into Python 3 - 0 views

www.diveintopython3.net/iterators.html

classes iterator decorator List Comprehensions python

shared by Benjamin Bandt-Horn on 30 Dec 13 - No Cached
  • Comprehensions are just a simple form of iterators. Generators are just a simple form of iterators
  • The first argument of every class method, including the __init__() method, is always a reference to the current instance of the class. By convention, this argument is named self.
  • self is not a reserved word in Python, merely a naming convention
  • ...6 more annotations...
  • To build an iterator from scratch, Fib needs to be a class, not a function.
  • in most cases), __iter__() simply returns self, since this class implements its own __next__() method.
  • a for loop will call this automatically, but you can also call it yourself manually
  • the __next__() method raises a StopIteration exception, this signals to the caller that the iteration is exhausted. Unlike most exceptions, this is not an error; it’s a normal condition that just means that the iterator has no more values to generate. If the caller is a for loop, it will notice this StopIteration exception and gracefully exit the loop. (In other words, it will swallow the exception.)
  • Do not use yield here; that’s a bit of syntactic sugar that only applies when you’re using generators. Here you’re creating your own iterator from scratch; use return instead
  • raise StopIteration
  • Benjamin Bandt-Horn on 30 Dec 13
     
    Comprehensions are just a simple form of iterators. Generators are just a simple form of iterators
Benjamin Bandt-Horn

How to implement __iter__(self) for a container object (Python) - Stack Overflow - 0 views

stackoverflow.com/...-for-a-container-object-python

container python iterator generator List Comprehensions

shared by Benjamin Bandt-Horn on 30 Dec 13 - No Cached
  • usually __iter__() just return self if you have already define the next() method (generator object)
  • While you are looking at the collections module, consider inheriting from Sequence, Mapping or another abstract base class if that is more appropriate. Here is an example for a Sequence subclass:
  • if hasattr(self.data[0], "__iter__": return self.data[0].__iter__() return self.data.__iter__()
  • Benjamin Bandt-Horn on 30 Dec 13
     
    if not self.data: raise StopIteration
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