Common Python Functions and Practical Code Examples

Beginners often get stuck when writing code because they cannot recall which built‑in functions to use; this article compiles a list of common Python functions to help them memorize and apply these tools efficiently.

1. Basic Functions

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

<span>f = 30.5<br/>ff = str(f)<br/>print(type(ff))<br/><br/># Output: class 'str'</span>

2. Flow Control

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

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

3. List Operations

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

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

4. Tuple Operations

Example: Slice a tuple, convert it to a list, modify the list, and convert back.

<span># Take elements with indices 1‑3 from the tuple and convert to list<br/>t = (1,2,3,4,5)<br/>print(t[1:4])<br/>l = list(t)<br/>print(l)<br/># Insert 6 at index 2 in the list<br/>l[2] = 6<br/>print(l)<br/># Convert back to tuple<br/>t = tuple(l)<br/>print(t)</span>

<span># Output:<br/>(2, 3, 4)<br/>[1, 2, 3, 4, 5]<br/>[1, 2, 6, 4, 5]<br/>(1, 2, 6, 4, 5)</span>

5. String Formatting

Three ways to use format():

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

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

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

6. Dictionaries

Example: Retrieve values with dict.get().

<span>d = {"name": "小黑"}<br/>print(d.get("name2", "没有查到"))<br/>print(d.get("name"))</span>

<span># Output:<br/>没有查到<br/>小黑</span>

7. Functions

Example: Define a function that creates a global variable.

<span>def fun1():<br/>    global b<br/>    b = 100<br/>    print(b)<br/>fun1()<br/>print(b)</span>

<span># Output:<br/>100<br/>100</span>

8. Processes and Threads

Example: Subclass threading.Thread and start two threads.

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

9. Modules and Packages

Example: Import a module from a package and use its attributes.

<span>from my_package1 import my_module3<br/>print(my_module3.a)<br/>my_module3.fun4()</span>

10. File Operations

(1) Regular file handling

Explanation of common file modes, attributes, and methods (illustrated with images).

(2) os module

Illustrates file‑system related functions (images omitted for brevity).

11. Decorators

Example: Using @classmethod inside a class.

<span>class B:<br/>    age = 10<br/>    def __init__(self, name):<br/>        self.name = name<br/>    @classmethod<br/>    def eat(cls):  # class method<br/>        print(cls.age)<br/><br/>    def sleep(self):<br/>        print(self)<br/><br/>b = B("小贱人")<br/>b.eat()</span>

# Output: 10

12. Regular Expressions

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

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

Conclusion

The purpose of this article is not to teach every function in depth but to help readers quickly memorize the names and purposes of frequently used Python functions; detailed usage can be looked up as needed, and repeated practice will solidify understanding.