1, def statements and parameters
Keywords python defined function is def, the following format:
def function name ([argument], [argument], ....) # value stored in the argument, after the function returns the argument will be destroyed.
2, return value and return statement
renturn function should return a value or expression # If you use an expression, the return value is the result of the expression evaluation
3, None value
None has a value referred to in Python, which represents no value. None is NoneType is a unique value data type, None must capitalize the first letter N. If you want something stored in the variable will not be confused with a real value, this value may not be useful. Return Value #Print () function is None
4, the local and global scope
Local variables: Variables and variable assignment in the function being called . # Local variables can not use the global scope, local scope can not use other local variable scope
Global variables: variable assignment outside of any function. # Global variables can be read in the local scope
Popular for local variables like you own something you can only use global variables are public, everyone is available, but you can not change the use and destruction of public things that really need to change if you need to submit application, python submit an application in a global statement.
Output:
5, Exception Handling
Python program encounters an error or "abnormal", which means the collapse of the entire program. If you want the program to be able to detect errors, process them, and then continue to run, then you must use the try and except statements to deal with the following format:
try :
Statement after the error block to be processed
the except: # you can use without any exception types except, but this is not a good way, through this program we can not identify the specific exception information. Because it captures all the exceptions.
Statements executed after an exception occurs
except <异常类别>,<参数> : #一个异常可以带上参数,可作为输出的异常信息参数。
出现异常后执行的语句
else : #异常处理可搭配else使用,如果没发生异常则执行else语句块。
else语句块
try-finally 语句
try-finally 语句无论是否发生异常都将执行最后的代码。
try :
<语句>
finally:
<语句> #退出try时总会执行
触发异常
我们也可以使用raise语句自己触发异常
raise语法格式如下:
raise [Exception [, args [, traceback]]] # 触发异常后,后面的代码就不会再执行
语句中 Exception 是异常的类型(例如,NameError)参数标准异常中任一种,args 是自已提供的异常参数。
最后一个参数是可选的(在实践中很少使用),如果存在,是跟踪异常对象。
用户自定义异常
通过创建一个新的异常类,程序可以命名它们自己的异常。异常应该是典型的继承自Exception类,通过直接或间接的方式。
class 自定义名字(异常基类)
def 函数名(参数):
语句块
python标准异常
异常名称 描述
BaseException 所有异常的基类
SystemExit 解释器请求退出
KeyboardInterrupt 用户中断执行(通常是输入^C)
Exception 常规错误的基类
StopIteration 迭代器没有更多的值
GeneratorExit 生成器(generator)发生异常来通知退出
StandardError 所有的内建标准异常的基类
ArithmeticError 所有数值计算错误的基类
FloatingPointError 浮点计算错误
OverflowError 数值运算超出最大限制
ZeroDivisionError 除(或取模)零 (所有数据类型)
AssertionError 断言语句失败
AttributeError 对象没有这个属性
EOFError 没有内建输入,到达EOF 标记
EnvironmentError 操作系统错误的基类
IOError 输入/输出操作失败
OSError 操作系统错误
WindowsError 系统调用失败
ImportError 导入模块/对象失败
LookupError 无效数据查询的基类
IndexError 序列中没有此索引(index)
KeyError 映射中没有这个键
MemoryError 内存溢出错误(对于Python 解释器不是致命的)
NameError 未声明/初始化对象 (没有属性)
UnboundLocalError 访问未初始化的本地变量
ReferenceError 弱引用(Weak reference)试图访问已经垃圾回收了的对象
RuntimeError 一般的运行时错误
NotImplementedError 尚未实现的方法
SyntaxError Python 语法错误
IndentationError 缩进错误
TabError Tab 和空格混用
SystemError 一般的解释器系统错误
TypeError 对类型无效的操作
ValueError 传入无效的参数
UnicodeError Unicode 相关的错误
UnicodeDecodeError Unicode 解码时的错误
UnicodeEncodeError Unicode 编码时错误
UnicodeTranslateError Unicode 转换时错误
Warning 警告的基类
DeprecationWarning 关于被弃用的特征的警告
FutureWarning 关于构造将来语义会有改变的警告
OverflowWarning 旧的关于自动提升为长整型(long)的警告
PendingDeprecationWarning 关于特性将会被废弃的警告
RuntimeWarning 可疑的运行时行为(runtime behavior)的警告
SyntaxWarning 可疑的语法的警告
UserWarning 用户代码生成的警告