Introduction
This section discusses mathematical calculations.
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This section discusses mathematical calculations.
Python has 4 types of numbers:
Booleans have two values: True
, False
.
a = True
b = False
Numerically, they're evaluated as integers with value 1
, 0
.
c = 4 + True ## 5
d = False
if d == 0:
print('d is False')
But, don't write code like that. It would be odd.
Signed values of arbitrary size and base:
a = 37
b = -299392993727716627377128481812241231
c = 0x7fa8 ## Hexadecimal
d = 0o253 ## Octal
e = 0b10001111 ## Binary
Common operations:
x + y Add
x - y Subtract
x * y Multiply
x / y Divide (produces a float)
x // y Floor Divide (produces an integer)
x % y Modulo (remainder)
x ** y Power
x << n Bit shift left
x >> n Bit shift right
x & y Bit-wise AND
x | y Bit-wise OR
x ^ y Bit-wise XOR
~x Bit-wise NOT
abs(x) Absolute value
Use a decimal or exponential notation to specify a floating point value:
a = 37.45
b = 4e5 ## 4 x 10**5 or 400,000
c = -1.345e-10
Floats are represented as double precision using the native CPU representation IEEE 754. This is the same as the double
type in the programming language C.
17 digits of precision
Exponent from -308 to 308
Be aware that floating point numbers are inexact when representing decimals.
>>> a = 2.1 + 4.2
>>> a == 6.3
False
>>> a
6.300000000000001
>>>
This is not a Python issue, but the underlying floating point hardware on the CPU.
Common Operations:
x + y Add
x - y Subtract
x * y Multiply
x / y Divide
x // y Floor Divide
x % y Modulo
x ** y Power
abs(x) Absolute Value
These are the same operators as Integers, except for the bit-wise operators. Additional math functions are found in the math
module.
import math
a = math.sqrt(x)
b = math.sin(x)
c = math.cos(x)
d = math.tan(x)
e = math.log(x)
The following comparison / relational operators work with numbers:
x < y Less than
x <= y Less than or equal
x > y Greater than
x >= y Greater than or equal
x == y Equal to
x != y Not equal to
You can form more complex boolean expressions using
and
, or
, not
Here are a few examples:
if b >= a and b <= c:
print('b is between a and c')
if not (b < a or b > c):
print('b is still between a and c')
The type name can be used to convert values:
a = int(x) ## Convert x to integer
b = float(x) ## Convert x to float
Try it out.
>>> a = 3.14159
>>> int(a)
3
>>> b = '3.14159' ## It also works with strings containing numbers
>>> float(b)
3.14159
>>>
Reminder: These exercises assume you are working in the ~/project
directory. Look for the file mortgage.py
.
Dave has decided to take out a 30-year fixed rate mortgage of $500,000 with Guido's Mortgage, Stock Investment, and Bitcoin trading corporation. The interest rate is 5% and the monthly payment is $2684.11.
Here is a program that calculates the total amount that Dave will have to pay over the life of the mortgage:
## mortgage.py
principal = 500000.0
rate = 0.05
payment = 2684.11
total_paid = 0.0
while principal > 0:
principal = principal * (1+rate/12) - payment
total_paid = total_paid + payment
print('Total paid', total_paid)
Enter this program and run it. You should get an answer of 966279.5999999957
.
Suppose Dave pays an extra $1000/month for the first 12 months of the mortgage?
Modify the program to incorporate this extra payment and have it print the total amount paid along with the number of months required.
When you run the new program, it should report a total payment of 929965.6199999959
over 342 months.
Modify the program so that extra payment information can be more generally handled. Make it so that the user can set these variables:
extra_payment_start_month = 61
extra_payment_end_month = 108
extra_payment = 1000
Make the program look at these variables and calculate the total paid appropriately.
How much will Dave pay if he pays an extra $1000/month for 4 years starting after the first five years have already been paid?
Modify the program to print out a table showing the month, total paid so far, and the remaining principal. The output should look something like this:
1 2684.11 499399.22
2 5368.22 498795.94
3 8052.33 498190.15
4 10736.44 497581.83
5 13420.55 496970.98
...
308 874705.88 3478.83
309 877389.99 809.21
310 880074.10 -1871.53
Total paid 880074.10
Months 310
While you're at it, fix the program to correct for the overpayment that occurs in the last month.
int()
and float()
can be used to convert numbers. For example,
>>> int("123")
123
>>> float("1.23")
1.23
>>>
With that in mind, can you explain this behavior?
>>> bool("False")
True
>>>
Congratulations! You have completed the Numbers lab. You can practice more labs in LabEx to improve your skills.