Python 3.7.4 (default, Aug 13 2019, 15:17:50) 
[Clang 4.0.1 (tags/RELEASE_401/final)] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> def square(x): return x*x
... 
>>> square(5)
25
>>> cows = square
>>> cows(5)
25
>>> # a function name is a variable name.
... # this name points at the code in memory that runs the function.
... 
>>> type(cows)
<class 'function'>
>>> 
(base) MAC:Mon Sep 14:09:43:week3> vi table.py
(base) MAC:Mon Sep 14:09:50:week3> python table.py
<tr><td>5</td><td>25</td></tr>

(base) MAC:Mon Sep 14:09:50:week3> !vi
vi table.py
(base) MAC:Mon Sep 14:09:56:week3> python table.py 
<tr><td>5</td><td>25</td></tr>

[1, 2, 3, 4, 5, 6] <function square at 0x7fddad62a200>
(base) MAC:Mon Sep 14:09:56:week3> !vi
vi table.py
(base) MAC:Mon Sep 14:09:56:week3> !p
python table.py 
<tr><td>5</td><td>25</td></tr>

None
(base) MAC:Mon Sep 14:09:56:week3> !vi
vi table.py
(base) MAC:Mon Sep 14:09:56:week3> !p
python table.py 
<tr><td>5</td><td>25</td></tr>

<table>
<tr><th>x</th><th>f(x)</th></tr>
<tr><td>1</td><td>1</td></tr>
<tr><td>2</td><td>4</td></tr>
<tr><td>3</td><td>9</td></tr>
<tr><td>4</td><td>16</td></tr>
<tr><td>5</td><td>25</td></tr>
<tr><td>6</td><td>36</td></tr>
</table>

(base) MAC:Mon Sep 14:09:56:week3> !vi
vi table.py
(base) MAC:Mon Sep 14:09:58:week3> python
Python 3.7.4 (default, Aug 13 2019, 15:17:50) 
[Clang 4.0.1 (tags/RELEASE_401/final)] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> def square(x): return x*x
... 
>>> str(square(
... ))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: square() missing 1 required positional argument: 'x'
>>> str(square)
'<function square at 0x7faddfe737a0>'
>>> 
(base) MAC:Mon Sep 14:10:00:week3> ls
table.py
(base) MAC:Mon Sep 14:10:00:week3> vi table.py
(base) MAC:Mon Sep 14:10:00:week3> python table.py
<tr><td>5</td><td>25</td></tr>

<table>
<tr><th>x</th><th>f(x)</th></tr>
<tr><td>1</td><td>1</td></tr>
<tr><td>2</td><td>4</td></tr>
<tr><td>3</td><td>9</td></tr>
<tr><td>4</td><td>16</td></tr>
<tr><td>5</td><td>25</td></tr>
<tr><td>6</td><td>36</td></tr>
</table>

<table>
<tr><th>x</th><th>f(x)</th></tr>
<tr><td>0.1</td><td>0.010000000000000002</td></tr>
<tr><td>0.2</td><td>0.04000000000000001</td></tr>
<tr><td>0.3</td><td>0.09</td></tr>
<tr><td>0.4</td><td>0.16000000000000003</td></tr>
<tr><td>0.5</td><td>0.25</td></tr>
<tr><td>0.6</td><td>0.36</td></tr>
</table>

(base) MAC:Mon Sep 14:10:00:week3> ls
table.py
(base) MAC:Mon Sep 14:10:02:week3> vi pancakes.py
(base) MAC:Mon Sep 14:10:03:week3> python pancakes.py
{'x': 5}
{'x': 5}
125
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <_frozen_importlib_external.SourceFileLoader object at 0x7f9fd8dc42d0>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, '__file__': 'pancakes.py', '__cached__': None, 'square': <function square at 0x7f9fd8e04320>, 'cube': <function cube at 0x7f9fd8e04440>, 'x': 5}
(base) MAC:Mon Sep 14:10:04:week3>