1. Python Introduction I#

Python’s core built-in objects#

Object type:

Examples:

Numbers

123, 3.14, math.pi, …

Strings

‘abc’, ‘EPFL’, “Geneva”, …

Lists

[1, [2, ‘troi’],4], list(range(99)

Dictionaries

{‘Apples’: 200, ‘Pears’: 123.5}, dict(hours=10)

Tuples

(x,y,z), (1, [2, ‘troi’],4)

Sets

set(‘abc’), {‘E’,’P’,’F’,’L’}

Other core types

Booleans, types, None

Files

open(‘data.txt’), open(r(‘/home/alex/abc.bin’),’wb’)

Program unit types

Functions, modules, classes

For more details check out the Python docs!

Here, we briefly summarize Numbers, Strings, Lists and Dictionaries.

Numbers in Python#

Python’s core objects include integers, floating-point, complex numbers, etc.

Types of numbers:

  • int represents integers, e.g. 2, 14213555

  • float represents reals, e.g. pi, 1.0, 0.000001

  • complex represents complex numbeers, e.g. real + imaginary

  • bool represents Boolean values, True and False

  • type() returns the type of Python objects

>>> type(5)           # again, ```>>>```m denotes what you type in a Python shell
int                   # here is the output!
>>> type(3.0)
float
>>> type(True)
bool
>>> complex(1,1)      # define a complex number
(1+1j)                # evaluates to this!
>>> complex(0,1)**2	  # remember: sqrt(-1) = j
(-1,0j)
>>> type(complex(1,1))
complex

Strings#

  • strings are concatenations of letters, special characters, numbers, and spaces

  • they are case sensitive!

  • strings can be defined by enclosing in quotation marks (”) or single quotes (‘).

Examples:

>>> S = 'Geneva'      # make a 6-character string and assign it to a name
>>> S = "Lausanne"    # make a 8-character string and assign it to a name
>>> S = str(3)        # cast integer 3 to string and assign to name
>>> type(S)
str

Lists#

  • ordered sequences of objects

  • accessible by index

  • have no fixed size and are very flexible

  • a list is denoted by square brackets []

Three examples:

list1=[0,1,2,3]
list2=[0,'abc']                               # lists can have mixed types; here int + str
list3=['EPFL','is','in',['Lausanne','VD']]    # they support arbitrary nesting

Dictionaries#

Dictionaries are

  • collections of key-value pairs that maps from keys to values.

  • the keys can be any immutable type, and the values can be any type.

  • like lists they can also be mixed and nested

  • a dict is denoted by curly brackets {}

An example:

inventory = {'Apples': 200, 'Pears': 123.5}