Commonly Used Python Functions: A Quick Reference Guide

Beginners often get stuck when coding because they cannot recall which built‑in function to use for a given task. To address this, a curated list of more than 100 frequently used Python functions is presented, covering everything from basic input/output to regular expressions, allowing quick review and deeper learning through practice.

1. Basic Functions

Example: Convert a floating‑point number to a string and print its type.

f = 30.5
ff = str(f)
print(type(ff))
# Output: class 'str'

2. Control Flow

Example: Determine a grade based on user‑entered score.

s = int(input("请输入分数:"))
if 80 >= s >= 60:
    print("及格")
elif 80 < s <= 90:
    print("优秀")
elif 90 < s <= 100:
    print("非常优秀")
else:
    print("不及格")
    if s > 50:
        print("你的分数在60分左右")
    else:
        print("你的分数低于50分")

3. Lists

Example: Find the index of the number 6 in a list.

l = [1,2,2,3,6,4,5,6,8,9,78,564,456]
n = l.index(6, 0, 9)
print(n)
# Output: 4

4. Tuples

Example: Modify a tuple by converting it to a list.

# Take three elements with indices 1~4 and convert to list
t = (1,2,3,4,5)
print(t[1:4])
l = list(t)
print(l)
# Insert 6 at index 2
l[2] = 6
print(l)
# Convert back to tuple
t = tuple(l)
print(t)
# Output:
# (2, 3, 4)
# [1, 2, 3, 4, 5]
# [1, 2, 6, 4, 5]
# (1, 2, 6, 4, 5)

5. Strings

Example: Three ways to use format() for string formatting.

Method 1 – Positional indices:

"{0} 嘿嘿".format("Python")
a = 100
s = "{0}{1}{2} 嘿嘿"
s2 = s.format(a, "JAVA", "C++")
print(s2)
# Output: 100JAVAC++ 嘿嘿

Method 2 – Empty braces:

a = 100
s = "{}{}{} 嘿嘿"
s2 = s.format(a, "JAVA", "C++", "C# ")
print(s2)
# Output: 100JAVAC++ 嘿嘿

Method 3 – Named placeholders:

s = "{a}{b}{c} 嘿嘿"
s2 = s.format(b="JAVA", a="C++", c="C# ")
print(s2)
# Output: C++JAVAC#  嘿嘿

6. Dictionaries

Example: Retrieve values from a dictionary with a default.

d = {"name": "小黑"}
print(d.get("name2", "没有查到"))
print(d.get("name"))
# Output:
# 没有查到
# 小黑

7. Functions

Custom functions are demonstrated, showing how a global variable defined inside a function can be accessed outside.

def fun1():
    global b
    b = 100
    print(b)
fun1()
print(b)
# Output:
# 100
# 100

8. Processes and Threads

Example: Create threads by subclassing threading.Thread.

# Multi‑thread creation
class MyThread(threading.Thread):
    def __init__(self, name):
        super().__init__()
        self.name = name
    def run(self):
        # Thread work
        for i in range(5):
            print(self.name)
            time.sleep(0.2)
# Instantiate threads
t1 = MyThread("凉凉")
t2 = MyThread("最亲的人")

t1.start()
 t2.start()

9. Modules and Packages

Example: Import a module from a package.

from my_package1 import my_module3
print(my_module3.a)
my_module3.fun4()

10. File Operations

(1) Regular file handling

Common file modes and file object attributes/methods are illustrated with diagrams.

11. Decorators

Example: Using @classmethod in a class.

class B:
    age = 10
    def __init__(self, name):
        self.name = name
    @classmethod
    def eat(cls):  # class method
        print(cls.age)
    def sleep(self):
        print(self)

b = B("小贱人")
b.eat()
# Output: 10

12. Regular Expressions

Example: Split a string using re.split().

import re
s = "abcabcacc"
l = re.split("b", s)
print(l)
# Output: ['a', 'ca', 'cacc']

Conclusion

The purpose of this article is not to teach every detail of each function, but to help readers quickly memorize the names and purposes of frequently used Python functions. Once you know what a function does, you can look up its exact usage as needed.

If you do not even know the function name, you will waste much more time searching for it.