Types and built-in functions¶
# Replace the value of this variable with your name
my_name = 'John Coltrane'
print(type(52))
print(type("52"))
print(type('52'))
print(type(52.0))
Every value has a type.¶
Every value in a program has a specific type.
Integer (
int): represents positive or negative whole numbers like 3 or -512.Floating point number (
float): represents real numbers like 3.14159 or -2.5.Character string (usually called “string”,
str): text.Written in either single quotes or double quotes (as long as they match).
The quote marks aren’t printed when the string is displayed.
Built-in functions¶
Use the built-in function
typeto find out what type a value has.Works on variables as well.
But remember: the value has the type — the variable is just a label.
def get_gdp(C,I,G,X,M):
return C + I + G + (X - M)
island_gdp = get_gdp(1000000, 500000,800000,100000,2000000)
print(island_gdp)
400000
Types control what operations (or methods) can be performed on a given value.¶
A value’s type determines what the program can do to it.
print(5 - 3)
print('hello' + ', ' + my_name)
You can use the “+” and “*” operators on strings.¶
“Adding” character strings concatenates them.
full_name = 'Ahmed' + ' ' + 'Walsh'
print(full_name)
Multiplying a character string by an integer N creates a new string that consists of that character string repeated N times.
Since multiplication is repeated addition.
separator = '=' * 10
print(separator)
Strings have a length (but numbers don’t).¶
The built-in function
lencounts the number of characters in a string.
print(len(full_name))
But numbers don’t have a length (not even zero).
print(len(52))
Must convert numbers to strings or vice versa when operating on them.¶
Cannot add numbers and strings.
print(1 + '2')
Not allowed because it’s ambiguous: should
1 + '2'be3or'12'?Some types can be converted to other types by using the type name as a function.
print(1 + int('2'))
print(str(1) + '2')
Can mix integers and floats freely in operations.¶
Integers and floating-point numbers can be mixed in arithmetic.
Python 3 automatically converts integers to floats as needed. (Integer division in Python 2 will return an integer, the floor of the division.)
print('half is', 1 / 2.0)
print('three squared is', 3.0 ** 2)