PYTHON SEQUENCE DIAGRAM GENERATOR GENERATOR

PYTHON SEQUENCE DIAGRAM GENERATOR GENERATOR

If only list comprehensions were available, and we needed to lazily build a set of items to be processed, we will have to write a generator function. Notice how a list comprehension looks essentially like a generator expression passed to a list constructor.īy allowing generator expressions, we don't have to write a generator function if we do not need the list. Alternately, we can think of list comprehensions as generator expressions wrapped in a list constructor.ġ # list comprehension 2 doubles = 3 4 # same as the list comprehension above 5 doubles = list( 2 * n for n in range( 50))

In fact, we can turn a list comprehension into a generator expression by replacing the square brackets ('') with parentheses.

Generator expressions provide an additional shortcut to build generators out of expressions similar to that of list comprehensions. The built-ins will always be much faster. Note: the above code is perfectly acceptable for expository purposes, but remember that in Python 2 firstn() is equivalent to the built-in xrange() function, and in Python 3 range() is an immutable sequence type.

It is very similar to the implementation that built a list in memory, but has the memory usage characteristic of the iterator implementation. Note that the expression of the number generation logic is clear and natural. 1 # a generator that yields items instead of returning a list 2 def firstn( n): 3 num = 0 4 while num < n: 5 yield num 6 num += 1 7 8 sum_of_first_n = sum( firstn( 1000000))

Python sequence diagram generator