Python3 input() Function

Python3 内置函数Python3 Built-in Functions

input()The function obtains user input from standard input (keyboard) and returns astring (str) type。

Note:input()Regardless of what is entered, the return value is always a string. If numerical calculations are needed, you must manually perform type conversion (e.g.,int()、float()）。

Function Syntax

input([prompt])

Parameter Description:

  • prompt：Optional, the message prompting the user for input

Example

input()Get user input and return it as a string.

input() Basic Usage

>>>name = input("Please enter your name:")Please enter your name: Xiao Ming >>>print("Hello,", name)Hello, Xiao Ming

Even if a number is entered, the return value is still a string.

Type Issues (Common Pitfalls)

>>>a = input("Please enter a number:")Please enter a number:123 >>> type(a) <class 'str'>

Note:Values obtained directly using input() cannot participate in numerical calculations.

Incorrect Example:

>>> a = input("请输入数字：")
>>> print(a + 1)
TypeError: can only concatenate str (not "int") to str

Correct Approach:

>>> a = int(input("请输入数字："))
>>> print(a + 1)

input() Receiving Multiple Values

split()Splits the input by spaces into an array of strings.

Example

# Enter multiple values (separated by spaces)
a, b, c = input("Please enter three numbers:").split()

# Convert types
a = int(a)
b = int(b)
c = int(c)

print(a, b, c)

Usemap()can complete type conversion in one step, making the code cleaner.

Recommended Approach (Advanced)

# Complete splitting + conversion in one step
a, b, c = map(int, input("Please enter three numbers:").split())

print(a, b, c)

Practice: Calculating Triangle Area

# Enter the three sides of the triangle
a, b, c = map(int, input("Please enter the lengths of the three sides of the triangle:").split())

# Calculate semi-perimeter
p = (a + b + c) / 2

# Calculate area using Heron's formula
s = (p * (p - a) * (p - b) * (p - c)) ** 0.5

print("The area of the triangle is:", format(s, '.2f'))

Running result:

请输入三角形三边的长：3 4 5
三角形面积为： 6.00

Common Usage Summary

  • input("提示"): Input with prompt
  • input(): Input without prompt
  • int(input()): Get integer
  • float(input()): Get float
  • input().split(): Get multiple strings
  • map(int, input().split()): Get multiple integers (recommended)

Differences between Python2 and Python3

In Python2:

  • raw_input(): Returns string
  • input(): Executes the expression (has security risks)

In Python3:

  • Only retainedinput()
  • Uniformly returns a string, safer and easier to understand

Core Summary

One-sentence summary: 

input() = 获取输入 + 返回字符串
  • Returns a string by default
  • Must convert types when participating in calculations
  • For multiple inputs, it is recommended to use split() + map()

Python3 内置函数Python3 Built-in Functions

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