Master Python Input & Output: From Basics to Practical Tricks

Why Input and Output Matter

From the classic "hello world" to more complex examples, a program becomes meaningful only when it can receive user input, process it, and display results on the screen.

Input Function

The input() function always returns a string, even if the user types a number. Simple examples illustrate this behavior:

# Example 1
inp = input("please input your name: ")
# User types: jack
print(inp)  # 'jack'
print(type(inp))  # <class 'str'>

# Example 2
age = input("please input your age: ")
print(age)  # '18'
print(type(age))  # <class 'str'>

# Example 3 (empty input)
empty = input("Enter something: ")
print(empty)  # ''

# Example 4 (preserve whitespace)
a = input("请输入一个字符：")
print(a)  # '   前后带有空白   '

Common handling patterns include:

# Prompt again if input is empty
inp = input("请输入你的姓名:  ")
if inp == "":
    inp = input("姓名不能为空，请重新输入:  ")

# Convert string to integer safely
age = input("请输入你的年龄：")
if age.isdigit():
    age = int(age)
    print("你的年龄是：", age)
else:
    print("输入不合法！")

# Strip whitespace
inp = input("请输入你的姓名:  ")
inp = inp.strip()
print(inp)

Input can also be used to pause program execution:

print("程序前面部分执行完毕......")
input("请按回车继续......")  # waits for Enter
print("继续执行程序的后面部分......")

Print Function

The print() function sends formatted text to standard output. It accepts multiple arguments separated by commas, automatically inserting spaces.

a = "i am"
b = "student"
print(a, "a", b)          # i am a student
print(a+"a"+b)            # i ama student

Key parameters:

sep : separator between arguments (default space).

end : string appended after the last value (default newline). Setting end='' prevents a line break.

print(a, "a", b, sep="*")  # i am*a*student

Formatted Output with % Operator

Python supports C‑style % formatting. Place format specifiers like %s or %d in a string and provide a tuple of values.

print("我叫 %s 今年 %d 岁!" % ("小明", 10))

Examples of various specifiers and mappings:

s = "i am %s" % "jack"
print(s)

s = "i am %s age %d" % ("jack", 18)
print(s)

s = "i am %(name)s age %(age)d" % {"name": "jack", "age": 18}
print(s)

s = "percent %.2f" % 99.97623
print(s)

s = "i am %(pp).2f" % {"pp": 123.425556}
print(s)

s = "i am %.2f %%" % 123.425556
print(s)

To print a literal percent sign, use %%.