Master Python Basics: Numbers, Strings, Functions, Data Structures, Classes & Tools

1. Numbers

1. Absolute value

Calculate the absolute value (or magnitude) of a number.

abs(-6)  # 6

2. Base conversion

Convert decimal numbers to binary, octal, and hexadecimal.

bin(10)   # '0b1010'
oct(9)   # '0o11'
hex(15)  # '0xf'

3. Integer ↔ ASCII

Convert between integer codes and ASCII characters.

chr(65)   # 'A'
ord('A')  # 65

4. All‑true check

Return True if every element in an iterable is truthy, otherwise False.

all([1, 0, 3, 6])   # False
all([1, 2, 3])      # True

5. Any‑true check

Return True if at least one element is truthy.

any([0, 0, 0, []])   # False
any([0, 0, 1])       # True

6. Boolean evaluation

Use bool() to evaluate truthiness of objects.

bool([0,0,0])   # True
bool([])        # False
bool([1,0,1])   # True

7. Complex numbers

Create a complex number.

complex(1, 2)   # (1+2j)

8. Quotient and remainder

Use divmod() to get both quotient and remainder.

divmod(10, 3)   # (3, 1)

9. Float conversion

Convert integers or numeric strings to float; raises ValueError on failure.

float(3)        # 3.0
float('a')      # ValueError

10. Integer conversion with base

Convert strings to integers with a specified base.

int('12', 16)   # 18

11. Power with modulus

Compute exponentiation with optional modulus.

pow(3, 2, 4)   # 1

12. Rounding

Round numbers to a given number of decimal places.

round(10.0222222, 3)   # 10.022
round(10.05, 1)       # 10.1

13. Chain comparison

Demonstrate Python's chained comparison operators.

i = 3
print(1 < i < 3)   # False
print(1 < i <= 3)  # True

2. Strings

14. String → bytes

Encode a string to bytes using UTF‑8.

bytes('apple', encoding='utf-8')   # b'apple'

15. Any object → string

Convert objects to their string representation.

str(100)      # '100'
str([])       # '[]'
str(tuple())  # '()'

16. Execute code from a string

Compile and execute a string as Python code.

s = "print('helloworld')"
r = compile(s, "<string>", "exec")
exec(r)   # prints helloworld

17. Evaluate an expression

Evaluate a string expression and return its result.

eval("1 + 3 + 5")   # 9

18. String formatting

Use format() to format strings.

"i am {0},age{1}".format("tom", 18)   # i am tom,age18

19. Formatting table examples

Showcase various format specifications (precision, padding, grouping, percentages, scientific notation, alignment).

3. Functions

19. Sorting

Sort lists directly or by a key.

a = [1,4,2,3,1]
sorted(a, reverse=True)   # [4,3,2,1,1]
students = [{'name':'xiaoming','age':18,'gender':'male'}, {'name':'xiaohong','age':20,'gender':'female'}]
sorted(students, key=lambda x: x['age'])   # sorted by age

20. Sum

Calculate the sum of an iterable, optionally with a start value.

a = [1,4,2,3,1]
sum(a)          # 11
sum(a, 10)      # 21

21. nonlocal keyword

Use nonlocal to modify a variable in an enclosing (non‑global) scope.

def wrapper():
    i = 0
    def inner():
        nonlocal i
        i += 1
        print(i)
    return inner

22. global keyword

Declare a variable as global to modify it inside a function.

i = 0

def h():
    global i
    i += 1
h()
print(i)   # 1

23. Swap two elements

Swap values using tuple unpacking.

def swap(a, b):
    return b, a
print(swap(1, 0))   # (0, 1)

24. Function objects list

Store functions in a list and call by index.

def f():
    print("i'm f")
def g():
    print("i'm g")
[ f, g ][1]()   # prints i'm g

25. Reverse sequence generation

Generate a descending list using range() with a negative step.

list(range(10, -1, -1))   # [10, 9, ..., 0]

26. Five types of function parameters

Demonstrate positional, keyword, default, *args, and **kwargs.

def f(a, *b, c=10, **d):
    print(f'a:{a}, b:{b}, c:{c}, d:{d}')

f(1, 2, 5, width=10, height=20)   # a:1, b:(2,5), c:10, d:{'width':10,'height':20}

27. Slice object

Use a slice object for reusable slicing.

perfect_slice = slice(1, 10, 2)
cake1 = list(range(5, 0, -1))
print(cake1[perfect_slice])   # [4, 2]

28. Lambda animation demo

Explain lambda functions with an example that finds the longest list.

def max_len(*lists):
    return max(*lists, key=lambda v: len(v))

r = max_len([1,2,3], [4,5,6,7], [8])
print(f'Longest list is {r}')   # [4,5,6,7]

4. Data Structures

29. Create a dictionary

Various ways to build dictionaries.

dict()
{'a':'a', 'b':'b'}
dict(zip(['a','b'], [1,2]))
dict([('a',1), ('b',2)])

30. Frozen set

Create an immutable set.

frozenset([1,1,3,2,3])   # frozenset({1,2,3})

31. Convert to set

Remove duplicates by converting a list to a set.

set([1,4,2,3,1])   # {1,2,3,4}

32. Slice object creation

Instantiate a slice and use it on a list.

my_slice = slice(0,5,2)
a = [1,4,2,3,1]
print(a[my_slice])   # [1,2,1]

33. Convert to tuple

Make an immutable tuple from a list.

i_am_tuple = tuple([1,3,5])   # (1, 3, 5)

5. Classes and Objects

34. Callable check

Use callable() to test if an object can be called.

callable(str)   # True
callable(int)   # True

35. __repr__ output

Define __repr__ to control the string representation of an instance.

class Student:
    def __init__(self, id, name):
        self.id = id
        self.name = name
    def __repr__(self):
        return f'id = {self.id}, name = {self.name}'

36. Class method

Use @classmethod to define a method that receives the class itself.

class Student:
    @classmethod
    def f(cls):
        print(cls)

37. Delete attribute

Remove an attribute with delattr() and check existence with hasattr().

delattr(xiaoming, 'id')
hasattr(xiaoming, 'id')   # False

38. List all attributes

Use dir() to list an object's attributes and methods.

dir(xiaoming)

39. Get attribute value

Retrieve an attribute dynamically with getattr().

getattr(xiaoming, 'name')   # 'xiaoming'

40. Attribute existence

Check if an object has a given attribute using hasattr().

hasattr(xiaoming, 'name')   # True
hasattr(xiaoming, 'address')   # False

41. Object identity

Get the memory address of an object with id().

id(xiaoming)

42. Instance test

Determine if an object is an instance of a class with isinstance().

isinstance(xiaoming, Student)   # True

43. Subclass test

Check inheritance relationships with issubclass().

class Undergraduate(Student):
    pass
issubclass(Undergraduate, Student)   # True

44. Root object

All classes inherit from object.

type(object())   # object

45. Property creation

Define managed attributes using property() or the @property decorator.

class C:
    def __init__(self):
        self._x = None
    @property
    def x(self):
        return self._x
    @x.setter
    def x(self, value):
        self._x = value
    @x.deleter
    def x(self):
        del self._x

46. Type inspection

Use type() to get an object's type.

type(xiaoming)   # __main__.Student

47. Metaclass concept

Explain that classes themselves are objects created by the metaclass type.

Student = type('Student', (), {})

6. Tools

48. Enumerate

Iterate with index using enumerate().

s = ['a', 'b', 'c']
for i, v in enumerate(s, 1):
    print(i, v)
# 1 a
2 b
3 c

49. Size of an object

Get memory consumption with sys.getsizeof().

import sys
a = {'a':1, 'b':2.0}
sys.getsizeof(a)   # e.g., 240

50. Filter

Filter elements using a predicate function.

fil = filter(lambda x: x>10, [1,11,2,45,7,6,13])
list(fil)   # [11, 45, 13]

51. Hash value

Obtain an object's hash with hash(). Mutable built‑ins are unhashable.

hash(xiaoming)   # e.g., 6139638
hash([1,2,3])   # raises TypeError

52. Help

Show documentation for an object using help().

help(xiaoming)

53. User input

Read a line from standard input with input().

name = input()   # user types "aa"

54. Create iterator

Convert an iterable to an iterator with iter().

lst = [1,3,5]
for i in iter(lst):
    print(i)

55. Open file

Open a file with various modes (r, w, x, a, b, t, +).

fo = open('D:/a.txt', mode='r', encoding='utf-8')
content = fo.read()

56. Range

Generate immutable sequences with range().

range(11)          # 0..10
range(0, 11, 1)   # same as above

57. Reversed iterator

Iterate backwards using reversed().

for i in reversed([1,4,2,3,1]):
    print(i)

58. Zip aggregation

Combine multiple iterables element‑wise with zip().

x = [3,2,1]
y = [4,5,6]
list(zip(y, x))   # [(4,3), (5,2), (6,1)]

59. Conditional operation

Choose a function based on a condition.

from operator import add, sub

def add_or_sub(a, b, oper):
    return (add if oper == '+' else sub)(a, b)

add_or_sub(1, 2, '-')   # -1

60. Object serialization

Serialize custom objects to JSON using json.dump() with a custom encoder.

import json
class Student:
    def __init__(self, **args):
        self.ids = args['ids']
        self.name = args['name']
        self.address = args['address']

xiaoming = Student(ids=1, name='xiaoming', address='北京')
xiaohong = Student(ids=2, name='xiaohong', address='南京')
with open('json.txt', 'w', encoding='utf-8') as f:
    json.dump([xiaoming, xiaohong], f, default=lambda obj: obj.__dict__, ensure_ascii=False, indent=2, sort_keys=True)