TIL about mutable python generator data

generator_with_mutable_data.py

"""
TIL data used/returned in python generators doesn't have any special mutability
properties - they're just like the rest of us!
"""

In [1]: def generator():
   ...:     result = [1, 2, 3, 4]
   ...:     while True:
   ...:         print "before", result
   ...:         yield result
   ...:         print "after", result
   ...:         

In [2]: gen = generator()

In [3]: data = gen.next()
before [1, 2, 3, 4]

In [4]: data
Out[4]: [1, 2, 3, 4]

In [5]: data.append(5)

In [6]: data
Out[6]: [1, 2, 3, 4, 5]

In [7]: gen.next()
after [1, 2, 3, 4, 5]
before [1, 2, 3, 4, 5]
Out[7]: [1, 2, 3, 4, 5]