Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 23 2015, 02:52:03) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "copyright", "credits" or "license()" for more information.
>>> WARNING: The version of Tcl/Tk (8.5.9) in use may be unstable.
Visit http://www.python.org/download/mac/tcltk/ for current information.

>>> # we have already seen one way to convert between types
>>> round(3.75)
4
>>> # casting: changing one type to another explicitly
>>> int(3.75)
3
>>> int(-3.75)
-3
>>> type(3.75)
<class 'float'>
>>> type(3)
<class 'int'>
>>> 
>>> float(42)
42.0
>>> type(42.0)
<class 'float'>
>>> 
>>> type("hello")
<class 'str'>
>>> 

>>> print("Exchange",i,":")
Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    print("Exchange",i,":")
NameError: name 'i' is not defined
>>> print("Exchange",3,":")
Exchange 3 :
>>> print("Exchange" + 3 + ":")
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    print("Exchange" + 3 + ":")
TypeError: Can't convert 'int' object to str implicitly
>>> str(3)
'3'
>>> print("Exchange", str(3) + ":")
Exchange 3:
>>> 
>>> str(4.5)
'4.5'
>>> x = input("Tell me a number: ")
Tell me a number: 4
>>> x
'4'
>>> int(x)
4
>>> 
>>> # int(), float(), str(), type()
>>> 
>>> # arithmetic operators (+,-,*,/ so far)
>>> 
>>> 5/2
2.5
>>> 5//2 # integer division
2
>>> 
>>> 5**2 # exponentiation
25
>>> 3**3 # 3^3
27
>>> 
>>> # mod operator
>>> 
>>> 5 % 2 # what is the remainder when 5 is divided by 2?
1
>>> 17 % 3
2
>>> 5 % 5
0
>>> 15 % 5
0
>>> 
>>> # sometimes floats with many decimal places produce errors
>>> 5.0 - 4.9
0.09999999999999964
>>> 

>>> 
>>> math.sqrt(2)
Traceback (most recent call last):
  File "<pyshell#46>", line 1, in <module>
    math.sqrt(2)
NameError: name 'math' is not defined
>>> import math
>>> math.sqrt(2)
1.4142135623730951
>>> math.sqrt(25)
5.0
>>> for * in math
SyntaxError: invalid syntax
>>> from math import *
>>> sqrt(2)
1.4142135623730951
>>> # do not do: from math import * (!!)
>>> 
>>> from math import sqrt
>>> sqrt(2)
1.4142135623730951
>>> 
>>> math.pi
3.141592653589793
>>> math.sin(0)
0.0
>>> math.cos(0)
1.0
>>> ================================ RESTART ================================
>>> 
Enter n = 10
##
>>> ================================ RESTART ================================
>>> 
Enter n = hello
Traceback (most recent call last):
  File "/Users/ssheehan/Desktop/triangle.py", line 10, in <module>
    main()
  File "/Users/ssheehan/Desktop/triangle.py", line 7, in main
    n = int(input("Enter n = "))
ValueError: invalid literal for int() with base 10: 'hello'
>>> ================================ RESTART ================================
>>> 
Enter n = 10.5
Traceback (most recent call last):
  File "/Users/ssheehan/Desktop/triangle.py", line 10, in <module>
    main()
  File "/Users/ssheehan/Desktop/triangle.py", line 7, in main
    n = int(input("Enter n = "))
ValueError: invalid literal for int() with base 10: '10.5'
>>> ================================ RESTART ================================
>>> 
Enter n = 10.5
##
>>> ================================ RESTART ================================
>>> 
Enter n = 4
##
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>>> ================================ RESTART ================================
>>> 
Enter n = 4
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>>> ================================ RESTART ================================
>>> 
Enter n = 4
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>>> ================================ RESTART ================================
>>> 
Enter n = 4
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######
>>> ================================ RESTART ================================
>>> 
Enter n = 10
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############
>>> ================================ RESTART ================================
>>> 
Enter n = 35
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#####################################
>>>