20 Common Python Built-in Constants with Example Code

When discussing Python's built-in constants, we refer to fixed values defined in built-in modules that are frequently used in programming.

True and False : Boolean constants representing logical true and false.

is_valid = True

if is_valid:

print("验证通过")

else:

print("验证失败")

None : Represents the absence of a value.

result = calculate_result()

if result is None:

print("计算结果不存在")

else:

print("计算结果为:", result)

NotImplemented : Indicates a method or functionality that has not been implemented.

class BaseClass:

def process_data(self):

raise NotImplementedError("该方法尚未实现")

class DerivedClass(BaseClass):

pass

obj = DerivedClass()

obj.process_data()

Ellipsis : Used to denote an omitted piece of code or logic.

def process_data(data):

if data == Ellipsis:

print("数据待补充")

else:

print("数据完整")

# 调用函数

process_data(...)

__debug__ : Boolean constant indicating whether the Python interpreter is running in debug mode.

def make_api_request():

url = "http://api.example.com"

# 在调试模式下输出请求的URL

if __debug__:

print("请求URL:", url)

# 发送API请求的代码

# ...

# 调用函数

make_api_request()

True and False integer values : True equals 1, False equals 0.

success = True

if success == 1:

print("操作成功")

else:

print("操作失败")

NotImplementedError : Exception class indicating an unimplemented method or functionality.

def process_data(data):

if data is NotImplemented:

raise NotImplementedError("该功能尚未实现")

else:

print("数据处理完成")

# 调用函数

process_data(NotImplemented)

StopIteration : Exception class indicating that an iterator has no more items.

data = [1, 2, 3]

iterator = iter(data)

while True:

try:

value = next(iterator)

print(value)

except StopIteration:

break

OverflowError : Exception class indicating a numeric overflow.

value = 10 ** 1000

print(value)

FloatingPointError : Exception class indicating a floating‑point operation error.

result = 1.0 / 0.0

print(result)

ZeroDivisionError : Exception class indicating division by zero.

result = 1 / 0

print(result)

ArithmeticError : Base class for numeric calculation errors.

try:

result = 1 / 0

print(result)

except ArithmeticError as e:

print("数值运算错误:", str(e))

EOFError : Exception class indicating end of input stream.

try:

data = input("请输入数据:")

print("输入的数据为:", data)

except EOFError:

print("输入流已结束")

IndentationError : Exception class indicating an indentation problem.

def process_data(data):

print(data)

TabError : Exception class indicating mixed tabs and spaces.

def process_data(data):

if data is None:

print("数据为空")

else:

print("数据为:", data)

# 调用函数

process_data( None)

UnicodeError : Exception class indicating Unicode‑related errors.

data = "中文"

encoded_data = data.encode("ascii")

print(encoded_data)

FileNotFoundError : Exception class indicating a missing file.

filename = "data.txt"

try:

with open(filename, "r") as file:

contents = file.read()

print(contents)

except FileNotFoundError:

print("文件不存在:", filename)

TypeError : Exception class indicating a type mismatch.

data = 100

length = len(data)

print(length)

ValueError : Exception class indicating an inappropriate value.

data = "abc"

integer_value = int(data)

print(integer_value)

AssertionError : Exception class indicating a failed assertion.

data = 10

assert data > 100, "数据不符合要求"

These example codes demonstrate the usage of twenty common Python built-in constants in real‑world automation tasks, helping developers write more efficient and readable code.