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Diffstat (limited to 'python.html.markdown')
| -rw-r--r-- | python.html.markdown | 51 |
1 files changed, 34 insertions, 17 deletions
diff --git a/python.html.markdown b/python.html.markdown index 2105748c..6c9da9a9 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -678,29 +678,46 @@ dir(math) ## 7. Advanced #################################################### -# Generators help you make lazy code +# Generators +# A generator "generates" values as they are requested instead of storing +# everything up front + +# The following method (*NOT* a generator) will double all values and store it +# in `double_arr`. For large size of iterables, that might get huge! def double_numbers(iterable): + double_arr = [] + for i in iterable: + double_arr.append(i + i) + +# Running the following would mean we'll double all values first and return all +# of them back to be checked by our condition +for value in double_numbers(range(1000000)): # `test_non_generator` + print value + if value > 5: + break + +# We could instead use a generator to "generate" the doubled value as the item +# is being requested +def double_numbers_generator(iterable): for i in iterable: yield i + i -# A generator creates values on the fly. -# Instead of generating and returning all values at once it creates one in each -# iteration. This means values bigger than 15 wont be processed in -# double_numbers. -# Note xrange is a generator that does the same thing range does. -# Creating a list 1-900000000 would take lot of time and space to be made. -# xrange creates an xrange generator object instead of creating the entire list -# like range does. -# We use a trailing underscore in variable names when we want to use a name that -# would normally collide with a python keyword -xrange_ = xrange(1, 900000000) - -# will double all numbers until a result >=30 found -for i in double_numbers(xrange_): - print i - if i >= 30: +# Running the same code as before, but with a generator, now allows us to iterate +# over the values and doubling them one by one as they are being consumed by +# our logic. Hence as soon as we see a value > 5, we stop break out of the +# loop and don't need to double most of the values sent in (MUCH FASTER!) +for value in double_numbers_generator(xrange(1000000)): # `test_generator` + print value + if value > 5: break +# BTW: did you notice the use of `range` in `test_non_generator` and `xrange` in `test_generator`? +# Just as `double_numbers_generator` is the generator version of `double_numbers` +# We have `xrange` as the generator version of `range` +# `range` would return back and array with 1000000 values for us to use +# `xrange` would generate 1000000 values for us as we request / iterate over those items + + # Decorators # in this example beg wraps say |