# # Types of numbers # 5 # -> 5 (integer) type(5) # -> <class 'int'> # integer type 2.5 # -> 2.5 (float) type(2.5) # -> <class 'float'> # floating point type 10**100 # -> 10000000000000000000000000000...000 # eg 10 to the power 100 is 1 followed by 100 zeros # integers can have any number of digits, 1/3 # -> 0.3333333333333333 # Floats have around 16 significant figures 2+3j # -> (2+3j) (complex number, j represents # imaginary number) type(2+3j) # -> <class 'complex'> # complex number type
# # Operators # 2 + 4 # -> 6 (addition) 7 - 3 # -> 4 (subtraction) 6 * 2 # -> 12 (multiplication) 5 / 2 # -> 2.5 (division) 2**3 # -> 8 (raise to the power, 2 to the power 3) (4 + 3) * 2 # -> 24 (brackets change priority) 5 // 2 # -> 2 (integer division always rounds down) -5 // 2 # -> -3 5 % 2 # -> 1 (modulo or remainder) 5.7 // 2.1 # -> 2.0 ( // works with floats, # always a whole number) 5.7 % 2.1 # -> 1.5 # % also works with floats, result is: # x % y = x - y * (x // y) # # int or float result? # 2.0 + 3 # -> 5.0 (if any input is a float, # the result will be a float) 2 + 3 # -> 5 (if all inputs are ints the # result will be an int) # EXCEPT: 6 / 3 # -> 2.0 (division always gives a float # even if the result is a whole number) 2**-2 # -> 0.25 (raising to a negative power # always gives a float)
a = 3 # variables don't need to be declared b = 1.2 # they are created when first assigned type(a) # -> <class 'int'> # variables don's have a type, but data does a = 2.5 # the same variable can be assigned different data types type(a) # -> <class 'float'> a = 'abc' # -> <class 'str'> see below type(a) # -> <class 'str'> see below xyz = 0 # variable names must start with a letter or my_val3 =1 # underscore, and may also contain numbers (but _a30 = 30 # not as the first character) alpha = 2 # by convention they only use lower case letters PI = 3.14 # or uppercase letters to indicate that they are # intended to be constant (Python doesn't actually # prevent these values from being altered)
'abc' # -> 'abc' (a text string) "abc" # -> 'abc' (double or single quotes are allowed)
int(3.7) # -> 3 (converts a float to an int) int(-3.7) # -> -3 (fractional part is truncated) int('12') # -> 12 (converts strings too) float(3) # -> 3.0 (converts an int to a float) float('1.5') # -> 1.5 (converts strings too) complex(1, 2) # -> (1+2j) (2 numbers to a complex number) complex('1+2j') # -> (1+2j) (converts strings too) complex('1 + 2j') # -> ERROR (spaces not allowed) str(3) # -> '3' (converts to string) str(1.5) # -> '1.5' (converts to string) str(1+2j) # -> '(1+2j)' (converts to string)
If you found this article useful, you might be interested in the book Functional Programming in Python, or other books, by the same author.
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