1. Declare exception syntax rules

• Try finally statement

try:
    Detection range
except Exception[as reason]:
    An exception occurred( Exception)Post processing code
finally:
    Code that will be executed anyway

A try statement can be matched with multiple except statements, because there may be multiple types of exceptions in the try statement block. Multiple except statements can be used to capture and handle the exceptions we are interested in respectively.

except (OSError, TypeError, ValueError) as reason:
  print('Error \n The reason for the error is:' + str(reason))

• raise statement

Used to declare an exception

>>> raise ZeroDivisionError('Exception with divisor zero')
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    raise ZeroDivisionError('Exception with divisor zero')
ZeroDivisionError: Exception with divisor zero

Example: try a new function int_input(), when the user inputs an integer, it returns normally. Otherwise, an error will be prompted and re input is required

def int_input(prompt=''):
	while True:
		try:
			int(input(prompt))
			break
		except ValueError:
			print('Error, the number you entered is not an integer!')

int_input("Please enter an integer:")

2. Use of else statement and with statement

• else statement

• Usage 1:

if a>b:
    print(a)
else:
    print(b)

• Usage 2:

#******************************************#
#  Judge the maximum common divisor of a given number. If it is a prime number, print it  #
#******************************************#
def showMaxFactor(num):
	count = num//2
	while count > 1:
		if num % count == 0:
			print('%d The largest divisor is%d' %(num,count))
			break
		count -= 1
	else:
	# Only after the loop is completed can it be executed. If break is used for execution in the loop, else will not be executed
		print('%d It's prime!' %num)

num = int(input('Please enter a number:'))
showMaxFactor(num)

• Usage III

try:
	print(int('abc'))
except ValueError as reason:
	print('Something went wrong:' + reason)
else:
	# If there is no error
	print('No exceptions!')

• with statement

with context_expression [as target(s)]:
    with-body

#**********************************#
#   Exception handling cooperation with sentence     	   #
#	It can avoid the situation that the opened file is not closed    #
#**********************************#
try:
	with open('data.txt', 'w') as f:
		for each_line in f:
			print(each_line)
except OSError as reason:
	print('Something went wrong:' + str(reason))

 

3.Python standard exception summary

Exception name	explain
AssertionError	Assert statement failure: when the condition behind the assert keyword is false, the program will throw this exception, which is generally used to put a checkpoint in the code >>> my_list = ['hello world'] >>>Assert len (my_list) > 0 # at this time, the program has no response >>> my_list.pop() >>>Assert len (my_list) > 0 # at this time, an exception AssertionError is thrown
AttributeError	Attempt to access an unknown object property: an exception thrown when the object property you are trying to access does not exist >>> my_list.fishc Throw an exception: AttributeError: 'list' object has no attribute 'fishc'
EOFError	This error basically means that it found an unexpected end of the file. (Ctrl+d on UNIX and Ctrl+Z+Enter on Windows)
FloatingPointError	Floating point calculation error
GeneratorExit	Gengeator. When the close () method is called
ImportError	When the import module fails
IndexError	Index is out of range for the sequence
KeyError	Find a keyword that does not exist in the dictionary
KeyboardError	User input interrupt key (Ctrl+c)
MemoryError	Memory overflow (memory can be released by deleting objects)
NameError	An attempt was made to access a variable that does not exist
NotImplementedError	Methods not yet implemented
OSError	An exception generated by the operating system (for example, opening a file that does not exist)
OverflowError	Numeric operation exceeds maximum limit
ReferenceError	A weak reference attempts to access an object that has been garbage collected
RuntimeError	General runtime error
StopIteration	The iterator has no more values
SyntaxError	Python syntax error
IndentationError	Indent error
TabError	Mixed use of Tab and space
SystemError	Python compiler system error
SystenExit	The Python compiler process was shut down
TypeError	Invalid operation between different types
UnboundLocalError	Access an uninitialized local variable (subclass of NameError)
UnicodeError	Unicode related error (subclass of ValueError)
UnicodeEncodeError	Error in Unicode encoding (subclass of Unicode error)
UnicodeDecodeError	Error in Unicode decoding (subclass of Unicode error)
UnicodeTranslateError	Error during Unicode conversion (subclass of Unicode error)
ValueError	Invalid parameter passed in
ZeroDivisionError	Divide by zero