Understanding Variable Definition and Usage in Python

In Python, understanding how to define and use variables is a fundamental programming skill, as variables act as containers for data such as numbers, strings, lists, and dictionaries.

Variable Definition

Defining a variable in Python is straightforward: you simply assign a value to a name without declaring its type, because Python is dynamically typed and determines the type at runtime.

Syntax:

variable_name = value

Here, variable_name is the identifier, = is the assignment operator, and value is the data stored.

Example 1: Define and print an integer variable

# Define an integer variable
age = 20
# Print the variable
print("年龄是:", age)

Example 2: Define and operate two float variables

# Define two float variables
height = 1.75
weight = 68.5
# Calculate BMI
bmi = weight / (height ** 2)
# Print BMI
print("体重指数(BMI)是:", bmi)

Example 3: String variable definition and concatenation

# Define two string variables
first_name = "张"
last_name = "三"
# Concatenate strings
full_name = first_name + last_name
# Print full name
print("全名是:", full_name)

Example 4: Boolean variable definition and conditional

# Define a boolean variable
is_student = True
# Conditional output
if is_student:
    print("是一个学生")
else:
    print("不是一个学生")

Example 5: List variable definition and element access

# Define a list variable
scores = [90, 85, 88, 92]
# Access first element
first_score = scores[0]
# Print first score
print("第一个成绩是:", first_score)

Example 6: Dictionary variable definition and key access

# Define a dictionary variable
person_info = {"姓名": "李四", "年龄": 25, "职业": "工程师"}
# Access age
age = person_info["年龄"]
# Print age
print("年龄是:", age)

Example 7: Variable reassignment

# Define an initial variable
counter = 0
# Reassign variable
counter = counter + 1
# Print updated count
print("更新后的计数值是:", counter)

Example 8: Swap values of two variables

# Define two variables
a, b = 1, 2
# Swap values
a, b = b, a
# Print swapped values
print("交换后a的值:", a)
print("交换后b的值:", b)

Example 9: Using input to receive user input

# Prompt user for name
name = input("请输入你的名字:")
# Print greeting
print("你好,", name)

Example 10: Multiple variables assignment

# Multiple assignment
x, y, z = 1, 2, 3
# Print values
print("x的值:", x)
print("y的值:", y)
print("z的值:", z)

These ten examples cover basic variable definitions and common operations, helping beginners grasp Python's core concepts.