Calling Builtin Functions

x = abs(y)
print(type(3.0))

Calling Functions From Modules

• Import an entire module

import math
print(math.sqrt(x**2 + y**2))

• Import a few functions from a module

from math import sqrt, 
print(sqrt(x**2 + y**2))
n = trunc(x))

• Import all functions from a module

from math import *
print(sqrt(x**2 + y**2))

Classes

• A class is an object that represents a type
• The type method returns the class object that represents the type of its argument
• The type of a class object is a class object called 'type'

>>> type("abc")
<class 'str'>
>>> type(type("abc"))
<class 'type'>
>>> type(int)
<class 'type'>
>>> type(type(int))
<class 'type'>

Methods

• A method is a function that “belongs to” an object
• Calling methods
• The method name is preceded by an object and a dot
• The object is actually passed as the first argument to the function

>>> s = "ABCD"
>>> s.lower()
'abcd'
>>> s = "abcd"
>>> s.upper()
'ABCD'

Object Expressions

• The object in a method call can be an expression that evaluates to the object

>>> ("abc" + "def").upper()
'ABCDEF'

String Methods

• s.capitalize() returns a capitalized version of s

>>> s = "abc"
>>> s.center(15)
'      abc      '

• s.count(s1) counts the number of occurrences of s1 in s

>>> s = "Now is the time for everyone to get a covid vaccination."
>>> s.count("t")
5
>>> s.count("on")
2

• s.endswith(s1) determines whether s ends with s1

>>> s = "image.pdf"
>>> s.endswith(".pdf")
True
>>> s.endswith(".jpg")
False

• s.find(s1) returns the position of the first occurrence of s1 in s or -1 if s1 does not occur

>>> s = "Now is the time for everyone to get a covid vaccination."
>>> s.find("t")
7
>>> s.find("ti")
11
>>> s.find("N")
0

• s.find(s1, m) starts the search at position m

>>> s.find("t", 10)
11

• s.find(s1, m, n) only searches between positions m and n

>>> s.find("t", 20, 30)
29
>>> s.find("t", 20, 25)
-1

• s.islower determines whether all characters in s are lower case

>>> s = "abc"
>>> s.islower()
True

• s.isupper() determines whether all characters in s are upper case

• s.isalpha() determines whether all characters in s are letter

• s.isdigit() determines whether all characters in s are digits (0 - 9)

• s.isspace() determines whether all characters in s are space, tab, or newline

• s.islower() determines whether all characters in s are lower case

• s.ljust(n) returns a string of length n starting with s (left justification)

• s.rjust(n) returns a string of length n ending with s (right justification)

>>> s = "abd"
>>> s.ljust(10)
'abd       '
>>> s.rjust(10)
'       abd'

• s.replace(s1, s2) returns a string like s but with s1 replaced by s2

>>> s="image.png";
>>> s.replace(".png", ".pdf")
'image.pdf'

• s.strip() returns a string like s but with white space removed from both ends

>>> s = "    foo   "
>>> s.strip()
'foo'

Chaining Method Calls

>>> s = "      foobar     "
>>> s.upper().replace("FOO", "xxx").strip()
'xxxBAR'

Special Methods

• There are special methods that are used by Python itself

• Their names are surrounded with double underscores

• Builtin functions are really special methods

>>> (-3).__abs__()
3
>>> "abcd".__len__()
4