Learn about Python Generators are very easy to implement, but a bit difficult to understand.

Generators are used to create iterators, but with a different approach. Generators are simple functions which return an iterable set of items, one at a time, in a special way.

When an iteration over a set of item starts using the for statement, the generator is run. Once the generator’s function code reaches a “yield” statement, the generator yields its execution back to the for loop, returning a new value from the set. The generator function can generate as many values (possibly infinite) as it wants, yielding each one in its turn.

Here is a simple example of a generator function which returns 7 random integers:

```import random

def lottery():
# returns 6 numbers between 1 and 40
for i in range(6):
yield random.randint(1, 40)

# returns a 7th number between 1 and 15
yield random.randint(1,15)

for random_number in lottery():
print("And the next number is... %d!" %(random_number))
```

#### Trinket.io on-line Python compiler

This function decides how to generate the random numbers on its own, and executes the yield statements one at a time, pausing in between to yield execution back to the main for loop.

# Exercise

Write a generator function which returns the Fibonacci series. They are calculated using the following formula: The first two numbers of the series are always equal to 1, and each consecutive number returned is the sum of the last two numbers. Hint: You can use only two variables in the generator function? Remember that assignments can be done simultaneously. The code will simultaneously switch the values of a and b: Try running the code and see for yourself.

```a = 1
b = 2
a, b = b, a
print(a,b)
```

#### Trinket.io on-line Python compiler

```# this is the answer code. see compiler below to create and run your solution.
def fib():
a, b = 1, 1
while 1:
yield a
a, b = b, a + b

# testing code
import types
if type(fib()) == types.GeneratorType:
print("Good, The fib function is a generator.")

counter = 0
for n in fib():
print(n)
counter += 1
if counter == 10:
break
```

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