50 Essential Python Built-in Functions and Their Usage

Python’s built‑in functions form the foundation of everyday programming. This guide lists fifty of the most useful built‑in functions, grouped by purpose, and provides short explanations together with runnable code examples.

1. Data Type Conversion Functions

int(), float(), str(), bool() convert values between common types.

num = int(3.14)
print(num)  # Output: 3

num = float(3)
print(num)  # Output: 3.0

string = str(123)
print(string, type(string))  # Output: 123 <class 'str'>

print(bool(0))   # Output: False
print(bool([1])) # Output: True

2. Numeric Operation Functions

abs(), round(), sum(), min(), max(), pow() perform basic arithmetic and aggregation.

print(abs(-5))               # 5
print(round(3.14159, 2))      # 3.14
print(sum([1, 2, 3]))         # 6
print(min([5, 3, 7]))         # 3
print(max([10, 15, 8]))       # 15
print(pow(2, 3))              # 8

3. Sequence Operation Functions

len(), sorted(), reversed(), enumerate(), zip() help manipulate iterable objects.

string = "hello"
print(len(string))            # 5

lst = [3, 1, 2]
print(sorted(lst))            # [1, 2, 3]

for x in reversed([1, 2, 3]):
    print(x)                  # 3 2 1

fruits = ["apple", "banana", "cherry"]
for index, fruit in enumerate(fruits):
    print(index, fruit)       # 0 apple ...

list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']
for pair in zip(list1, list2):
    print(pair)               # (1, 'a') (2, 'b') (3, 'c')

4. Input/Output Functions

print() displays output; input() reads user input.

print("Hello", "World")   # Hello World

user_input = input("请输入内容: ")
print(user_input)

5. File Operation Functions

open(), file.read(), file.write() manage file I/O.

file = open('test.txt', 'w')
file.write("Hello, file!")
file.close()

file = open('test.txt', 'r')
content = file.read()
print(content)
file.close()

6. String Handling Functions

capitalize(), upper(), lower(), strip(), split(), join() process text.

s = "python is fun"
print(s.capitalize())       # Python is fun

print("hello".upper())       # HELLO
print("WORLD".lower())       # world

s = "  python  "
print(s.strip())             # python

csv = "apple,banana,cherry"
print(csv.split(','))       # ['apple', 'banana', 'cherry']

lst = ['a', 'b', 'c']
print(''.join(lst))          # abc

7. Function‑Related Keywords

def defines a function; lambda creates anonymous functions; help() shows documentation.

def add(a, b):
    return a + b

add = lambda x, y: x + y
print(add(3, 4))            # 7

help(len)

8. Miscellaneous Utility Functions

range(), isinstance(), filter(), map(), all(), any(), id(), type(), dir(), globals(), locals(), eval(), exec(), format(), hash(), memoryview(), next() provide assorted capabilities.

for i in range(5):
    print(i)                # 0 1 2 3 4

print(isinstance(5, int))   # True

lst = [1, 2, 3, 4, 5]
print(list(filter(lambda x: x % 2 == 0, lst)))  # [2, 4]

print(list(map(lambda x: x * 2, [1, 2, 3])))   # [2, 4, 6]

print(all([True, True, False]))               # False
print(any([False, False, True]))               # True

obj = 10
print(id(obj))
print(type('hello'))
print(dir([1,2,3]))
print(globals())
print(locals())

result = eval('1 + 2 * 3')
print(result)                                 # 7

exec("print('Hello, exec!')")

name = "Alice"
age = 25
print("我的名字是{}，今年{}岁。".format(name, age))

print(hash('hello'))

byte_data = bytes([1,2,3])
mv = memoryview(byte_data)
print(mv)

it = iter([1,2,3])
print(next(it))                               # 1

Mastering these fifty built‑in functions will greatly improve coding efficiency and enable you to write cleaner, more Pythonic code.