Add samplegenerators.py

samplegenerators.py

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+# Generators hold values that are fetched lazily. 
+# Meaning that the entire collection isn't stored
+# in memory all at once, but rather retrieved when
+# needed.
+
+# This is best used when dealing with a large 
+# collection of items. Such as rows returned from 
+# a database call or looping over a large csv. 
+
+# Generators are intelligent enough to handle these
+# large collections without running out of memory. 
+# They dispose of variables in memory that are no
+# longer used and do not worry about variables
+# that are not yet needed.
+
+# Here's the syntax for a generator. It's just a
+# function! Take note of the yield keyword. yield
+# basically means 'return', but lets Python know
+# we'll be coming back for more. 
+def color_generator():
+    yield 'blue'
+    yield 'orange'
+    yield 'yellow'
+    yield 'purple'
+
+# One way to use generators is by calling `next()`
+# on it's instance
+g = color_generator()  # create the instance
+next(g)  # 'blue'
+next(g)  # 'orange'
+next(g)  # 'yellow'
+next(g)  # 'purple'
+
+# However, once a generator is exhausted, it will
+# not start back at the beginning. 
+next(g)  # Raises StopIteration error.
+
+# They're also iterables. No StopIteration errors
+# are thrown with this method. 
+for color in color_generator():
+    print(color)
+
+# 'blue'
+# 'orange'
+# 'yellow'
+# 'purple'
+