The document discusses various built-in functions in Python including: - Functions like max(), min(), len() that operate on lists, strings, etc. - Type conversion functions like int(), float(), str(). - Random number generating functions random(), randint(), choice(). - Other functions like abs(), round(), eval() for calculations, type conversions. - Indexing/slicing operations using [] on strings and lists to extract parts.

1. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Functions

2. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Functions
• A function is a named sequence of statements that performs a
computation.
• When you define a function, you specify the name and the
sequence of statements. Later, you can “call” the function by name.
• We have already seen one example of a function call:
>>> type(32)
<class 'int'>
• The name of the function is type. The expression in parentheses is
called the argument of the function.
• The argument is a value or variable that we are passing into the
function as input to the function.
• The result, for the type function, is the type of the argument.

3. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Built-in functions
• Python provides a number of important built-
in functions that we can use without needing
to provide the function definition.
• The creators of Python wrote a set of
functions to solve common problems and
included them in Python for us to use.
• The max and min functions give us the largest
and smallest values in a list, respectively:

4. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
>>> max('Hello world')
'w'
>>> min('Hello world')
' ‘
>>> min(2, 3)
2
>>> min(5, 6, 2.2, 17)
2.2
• The max function tells us the “largest character”
in the string (which turns out to be the letter “w”)
• and the min function shows us the smallest
character (which turns out to be a space).

5. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• Another very common built-in function is the len
function which tells us how many items are in its
argument.
• If the argument to len is a string, it returns the number
of characters in the string.
>>> len('Hello world')
11
>>>
• These functions are not limited to looking at strings.
>>> len(‘ha’ * 4)
8
• You should treat the names of built-in functions as
reserved words (i.e., avoid using “max” as a variable
name).

6. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Type conversion functions
• Python also provides built-in functions that convert values from one type to
another.
• The int function takes any value and converts it to an integer, if it can, or
complains otherwise:
>>> int('32')
32
>>> int('Hello')
ValueError: invalid literal for int() with base 10: 'Hello'
• int can convert floating-point values to integers, but it doesn’t round off; it
chops off the fraction part:
>>> int(3.99999)
3
>>> int(-2.3)
-2
>>> 8.7 * 10.52
91.523999999999987
>>> int(8.7 * 10.52)
91

7. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• float converts integers and strings to floating-point
numbers:
>>> float(32)
32.0
>>> float('3.14159')
3.14159
• Finally, str converts its argument to a string:
>>> str(32)
'32'
>>> str(3.14159)
'3.14159'

8. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Random numbers
• Given the same inputs, most computer
programs generate the same outputs every
time, so they are said to be deterministic.
• Determinism is usually a good thing, since we
expect the same calculation to yield the same
result.
• For some applications, we want the computer
to be unpredictable. Games are an obvious
example, but there are more.

9. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
import random
for i in range(10):
x = random.random()
print(x)
• The function random returns a random float
between 0.0 and 1.0 (including 0.0 but not
1.0). Each time you call random, you get the
next number in a long series.
• This program produces the following list of 10
random numbers between 0.0 and up to but
not including 1.0.

10. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• The random function is only one of many
functions that handle random numbers.
• The function randint takes the parameters low
and high, and returns an integer between low
and high (including both).
>>> random.randint(5, 10)
5
>>> random.randint(5, 10)
9

11. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• To choose an element from a sequence at
random, you can use choice:
>>> t = [1, 2, 3]
>>> random.choice(t)
2
>>> random.choice(t)
3

12. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
abs()
• For example, the abs operation returns the
absolute value of the argument:
>>> abs(-3)
3
>>> abs(2 – 3 * 7) # first calculate 2-3*7, which
is -19
19

13. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Round()
• Rounds the result to the nearest value.
• There is a function that will do this, but for a
floating-point argument it returns a floating-point
result:
>>> round(8.7 * 10.52)
92.0
• We can combine round and int to return a value
that is both rounded and integer:
>>> int(round(8.7 * 10.52))
92

14. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Eval()
• The function eval takes a string, interprets it as
an expression, and returns the result.
>>> eval (“42+2”)
44

15. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
input() and eval()
• An extremely useful function is input. This
function takes as argument a prompt.
• It prints the prompt, waits for the user to
respond, and returns as a string the value typed.
>>expr=input("enter expr:")
Enter expr:3+6
>>eval(expr)
9

16. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Indexing (Slicing)
• Another common operation uses the square brackets. This
is termed indexing, or slicing.
• An index or slice returns a portion of a larger value.
• In a string this can be used to produce a substring.
• Index values start at zero, and extend upwards to the
number of characters in the string minus one.
• When a single argument is given it is one character out of
the string.
• When two integers are written, separated by a colon, it is
termed a slice.
• The second value is an ending position. A portion of the
string starting at the given position up to but not including
the ending position is produced.

17. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
'realtor'[2:6]
Out[37]: 'alto'
'realtor'[2:7]
Out[38]: 'altor'
'realtor'[2:8]
Out[39]: 'altor'
'realtor'[2:3]
Out[40]: 'a'
'realtor'[2]
Out[41]: 'a'

18. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• If a colon is given but the last number is
omitted the result is the remainder of the
string starting from the given position.
>>> ‘recurrent’[2:]
‘current’
• Finally, if no number is given before the colon
the result is the initial string up to but not
including the given position.
>>> ‘halter’[:4]
‘halt’

19. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
• String are immutable, meaning they cannot be
changed once assigned.
• Instead, a new string constructed out of an
existing string can be formed in parts, using slicing
commands.
>>> word = 'red'
>>> word[1] = 'a‘ # show word cannot be changed
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: object doesn't support item assignment
>>> word = 'b' + word[:2] + 'a' + word[2:]
>>> word # change red to bread
'bread'

20. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
Exercises
1. Write python program to find the roots of the
quadratic equation.
– > x = -b +- sqrt(b2 – 4ac) / 2a

21. Dr. Harish Kumar B T, Dept of CSE, BIT, Bangalore
import math
a = input('type the value for the coefficient a')
b = input('type the value for the coefficient b')
c = input('type the value for the coefficient c')
ia=int(a)
ib=int(b)
ic=int(c)
d = math.sqrt(ib*ib-4*ia*ic)
id=float(d)
print('first root is ', (-ib + id) / (2 * ia))
print('second root is ', (-ib - id) / (2 * ia))