🔧 Built-in Functions: min(), max(), abs()

Python includes many pre-defined functions that are ready to use. A programmer doesn’t need to see their implementation — it’s hidden. It’s enough to know what these functions are called and what they do.

We have already encountered several built-in functions:

• print() — display output on the screen
• input() — read from the keyboard
• int() — convert to an integer
• float() — convert to a floating-point number

Now we explore three more built-in functions frequently used when working with numbers.

📌 The min() and max() Functions

The min() function returns the smallest value among its arguments, while max() returns the largest value.

min(value1, value2, value3, ...)
max(value1, value2, value3, ...)

Important: These functions can take any number of arguments, as long as all arguments support comparison operations (e.g., integers and floats can be compared, but floats and strings cannot).

a = max(3, 8, -3, 12, 9)
b = min(3, 8, -3, 12, 9)
c = max(3.14, 2.17, 9.8)
 
print(a)   # 12
print(b)   # -3
print(c)   # 9.8

📌 The abs() Function

The absolute value (or modulus) of a number is defined as:

• The number itself, if it is positive or zero.
• The opposite of the number, if it is negative.

Mathematically: |a| = a if a ≥ 0, and |a| = -a if a < 0.

In Python, the abs() function returns the absolute value of a number.

print(abs(10))      # 10
print(abs(-7))      # 7
print(abs(0))       # 0
print(abs(-17.67))  # 17.67

📝 The String Data Type (str)

The string data type, named str (short for "string" — a sequence of characters), is used to represent text in Python.

📌 Creating Strings

Python allows both single quotes ' and double quotes " for creating strings. This is useful when you need to include quotes inside the string.

s1 = 'Python rocks!'
s2 = "Python rocks!"          # Both are valid
s3 = "'Multi-line string example'"
 
# Including quotes inside strings:
s4 = 'She said "Hello"'
s5 = "He said 'Goodbye'"

📌 Empty Strings

An empty string contains no characters.

empty = ''     # Empty string
space = ' '    # String with one space — not empty!

📏 String Length — The len() Function

The length of a string is the number of characters it contains. The built-in function len() calculates this.

s1 = 'abcdef'
length1 = len(s1)                  # 6
length2 = len('Python rocks!')     # 13
 
print(length1)   # 6
print(length2)   # 13

🔢 Converting Numbers to Strings — The str() Function

We have already used int() and float() to convert strings to numbers. For the reverse operation — converting a number to a string — we use the str() function.

num1 = 1777    # integer
num2 = 17.77   # floating-point number
 
s1 = str(num1)   # '1777'
s2 = str(num2)   # '17.77'
 
print(type(s1))  # <class 'str'>
print(type(s2))  # <class 'str'>

➕ String Operations — Concatenation

Strings can be added together. The operation of adding strings is called concatenation.

s1 = 'ab' + 'bc'
s2 = 'bc' + 'ab'
s3 = s1 + s2 + '!!!'
 
print(s1)   # 'abbc'
print(s2)   # 'bcab'
print(s3)   # 'abbcbcab!!!'

print('ab' + 'bc')   # 'abbc'
print('bc' + 'ab')   # 'bcab' — different result!

📌 Using Concatenation for Output

Both approaches produce the same output:

# Both produce the same output:
print('a', 'b', 'c', sep='*', end='!')
print()
print('a' + '*' + 'b' + '*' + 'c' + '!')

a*b*c!
a*b*c!

🔁 String Repetition — Multiplying Strings

Python allows you to multiply a string by a non-negative integer. This operator repeats the string the specified number of times.

s = 'Hi' * 4
print(s)   # 'HiHiHiHi'
 
# Print a line of 75 dashes
print('-' * 75)

print('Hello' * 0)   # '' (empty string)
print('Hello' * 1)   # 'Hello' (unchanged)

🔍 The in Operator — Checking Substrings

The in operator checks whether one string is contained within another string.

s = 'https://python.org/'
 
if 'a' in s:
    print('The string contains the character "a"')
else:
    print('The string does not contain the character "a"')

The string does not contain the character "a"

📌 Using in with not

We can combine in with the not operator:

s = input()
 
if '.' not in s:
    print('The string does not contain a dot')
else:
    print('The string contains a dot')

📌 Simplifying Conditions with in

Instead of writing long conditions with multiple or operators, we can use in.

s = input()
if s == 'a' or s == 'e' or s == 'i' or s == 'o' or s == 'u':
    print('YES')

s = input()
if len(s) == 1 and s in 'aeiou':
    print('YES')

📌 Exact Substring Matching

The in operator checks for exact sequence matching — characters must be in the same order and consecutive.

print('ab' in 'abc')   # True — 'ab' appears exactly
print('ac' in 'abc')   # False — 'a' and 'c' are not consecutive

📌 Case Sensitivity

The in operator is case-sensitive.

s = 'Alpha'
print('p' in s)   # True — lowercase 'p' exists
print('P' in s)   # False — uppercase 'P' does not exist

🔢 The math Module

One of Python's advantages is the large number of ready-to-use functions. These functions are organised into modules. A module is a library of functions that can be imported into your program.

The math module is one of the most important in Python. It provides extensive functionality for performing calculations with real numbers.

📌 Importing the Module

import math
 
num1 = math.sqrt(2)     # square root of 2
num2 = math.ceil(3.8)   # round up
num3 = math.floor(3.8)  # round down
 
print(num1)   # 1.4142135623730951
print(num2)   # 4
print(num3)   # 3

📌 Importing Specific Functions

If you want to avoid typing the module name each time, you can import specific functions.

from math import sqrt, ceil
 
print(sqrt(25))     # 5.0
print(ceil(3.8))    # 4
# print(floor(3.8)) # Error — floor is not imported

Alternative — Import Everything:

from math import *
 
print(sqrt(25))     # 5.0
print(ceil(3.8))    # 4
print(floor(3.8))   # 3

Best practice: While from math import * is convenient, it's generally better to import only what you need, or import the whole module with import math. This makes your code more readable and avoids namespace conflicts.

📌 Commonly Used Functions in the math Module

Rounding functions:

Roots, powers, and factorial:

Trigonometric functions:

📌 Constants in the math Module

The math module also provides important mathematical constants:

import math
 
radius = 5
area = math.pi * radius ** 2
print(area)   # 78.53981633974483

🔽 Rounding Functions — Comparison

Python provides several ways to round numbers. Choose based on your needs.

📌 Comparison Table

Interesting fact: The round() function uses "banker's rounding" (round half to even) to reduce bias in statistical calculations. This is different from the rounding taught in many schools.