Simple types, variables

Simple types, variables#

Education objectives

  • int, bool, float, complex, NoneType

  • True, False, None

  • Keyword is, and, or and not

  • Notions of objects and attributes (with complex)

int (integers)#

a = 4
c = -10

# binary notation (base 2)
b = 0b010

# octal notation (base 8)
o = 0o011

# hexadecimal (base 16)
h = 0x1CF0

a = int("1")  # base 10
a = int("111", 2)  # base 2
a = int("70", 8)  # base 8
a = int("16", 16)  # base 16

Note

int in Python 3 are impressive! No limit! See https://docs.python.org/3.1/whatsnew/3.0.html#integers

Arithmetic operations#

print(10 + 3)
print(10 - 3)
print(10 * 3)
print(10 / 3)  # float division
print(10 // 3)  # integer division
print(10 % 3)

13
7
30
3.3333333333333335
3
1

bool (booleans)#

b = bool("1")
b = False
b = True

None, NoneType#

None is defined globally. The type of None is NoneType. This variable is typically used to represent something that is irrelevant, not initialized, ….

None evaluates to False.

# define a variable nb_students that is not yet defined
nb_students = None
# code that update nb_students

Comparison operations (bool)#

  • == equal

  • != différent

  • < inferior

  • <= inferior or equal

  • > superior

  • >= superior or equal

Keyword is: check identity#

a = None
print(a is None)
print(a is not None)

True
False

Keywords and and or#

True and True

True

True and False

False

False and False

False

True or True

True

True or False

True

False or False

False

float (real, double precision) and complex#

# float
a = float("1")
a = 1.234
a = 1e2
a = -1e-2
a = 0.2

# complex (2 floats)
c = complex("1")
c = 1 + 2j
print(c, c.real, c.imag, c.conjugate())

(1+2j) 1.0 2.0 (1-2j)

Note

Notation var_name.attr_name to access to an attribute of an object.

Warning about floating-point arithmetic and numerical errors!

b = 1e16
c = 1.2 + b
d = c - b
print(d)

gives 2.0. It’s a very general issue (not Python): see https://en.wikipedia.org/wiki/Floating-point_arithmetic.

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