Variables & numbers
- Video: Learning Python (2018 edition) 01: Your first programs (Variables, numbers, strings & casting)
Python supports all the basic arithmetic calculations
print( 2 + 2 ) print( 1.5 + 2.25 ) print( 7 - 2 ) print( 3 * 4 ) print( 10 / 2 ) print( 4 ** 3 ) # Exponent operator
A note about division & modulus
print( 13 / 5 ) # Real number divison print( 13 // 5 ) # Integer divison print( 13 % 5 ) # Modulus
Variables are just a named memory location
Defining a variable in Python is as simple as assigning a value to a name.
a = 10
- Names must start with an alpha character or underscore, but may then contain numeric characters.
- Names should be meaningful. Establish good habbits early. It should be obvious from the name of the variable what it's purpose is.
- Python's preferred practice is to separate_words_with_underscores rather than using camelCase like otherLanguages.
- Be warned variable names are case sensitive.
Variableis not the same as
var = 10 print(Var) # Will not work!
Using variables in calculations
Calculations can be assigned on a right goes into left basis.
val = 5 + 3 print(val)
Variables can be used as part of a calculation as well
a = 5 + 3 b = a * 4 c = a - b print( c ** a )
Integers vs real numbers
It is possible to denote the value of a variable to be a real number simply by adding a decimal element.
To convert a real number to integer, use the
int() command to truncate, or
round() to round.
a = 13.6 b = int(a) c = round(a) print(a,b,c)
To convert an integer to real, use the
a = 13 b = float(a) print(a,b)
Other numerical functions
import math answer = math.pi # π = 3.141592 answer = math.e # the natural number, e = 2.718281 answer = math.sqrt(100) # Square root answer = math.gcd(104,64) # Greatest common divisor answer = math.log(1024,2) # Log of base 2 answer = math.hypot(6,8) # Hypothenus of triangle with sides 6, 8 answer = math.cos( angle ) # Cosine of angle (radians) answer = math.sin( angle ) # Sine of angle (radians) answer = math.tan( angle ) # Tangent of angle (radians) answer = math.acos( adj/hypot ) # Arc-cosine in radians answer = math.asin( opp/hypot ) # Arc-sine in radians answer = math.atan( opp/adj ) # Arc-tan in radians answer = math.degrees( rad ) # Convert radians to degrees answer = math.radians( deg ) # Convert degrees to radians answer = abs( val ) # Absolute value import random num = random.randint(0,100) # Random number between 0 and 99 inclusive
The following questions assume you will use variables as the inputs into the problem, so the problems can re-caclulate solutions by changing the value assigned to the variable. You should also print the given information in your answer.
- For any given number, extract the 10s digit. For example,
The tens digit in 1234 is 3.
- Area of a right angled triangle calculator. Given values for
height, print the area.
- For any two digit number, swap the position of the digits. For instance,
- For any three digit number, print the sum of the three digits. For instance
- For any given year, print the century that year belongs to. Remember that 1999 and 2000 were the 20th century, whereas 2001 was the beginning of the 21st century.
- Given a number representing the number of seconds since midnight, print the time in 24hour clock format. For example
70500seconds should print a time of
- Area of a non-right angled triangle calculator. Given values for length
band angle in degrees
C, return the area of the triangle (remember you will have to convert degrees to radians first).
- For any given values for
c, will provide the solutions to the quadratic formula (you may assume both solutions are required). Be careful with your order of precedence. Here is an example solution set for testing: If
y=2x^2-4x-10then the solutions are