Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about the magic methods and exception handling in the foundation of Python. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

one。 Magic method 1. Attribute access

Usually you can pass the dot (.) Operator to access the properties of the object.

Class C: def _ init__ (self): self.x='X-man'c=C () c.x'X-man'getattr (c,'x', 'not having this attribute') 'X-man'getattr (c,' y', 'not having this attribute') 'not having this attribute'

Magic method:

(1) define the behavior when a user tries to get an attribute that does not exist.

_ _ getattr__ (self,name)

(2) define the behavior when the properties of the class are accessed.

_ _ getattribute__ (self,name)

(3) define the behavior when a property is set.

_ _ setattr__ (self,name,value)

(4) define the behavior when an attribute is deleted.

_ _ delattr__ (self,name) 2. Descriptor

(1) used to access the property, which returns the value of the property.

_ _ get__ (self,instance,owner)

(2) it will be called in the property assignment operation and nothing will be returned.

_ _ set__ (self,instance,value)

(3) controls the deletion operation and returns nothing.

_ delete__ (self,instance) class MyDescriptor: def _ get__ (self,instance,owner): print ("getting...", self,instance,owner) def _ set__ (self,instance,value): print ("setting...", self,instance,value) def _ delete__ (self,instance): print ("deleting...", self,instance) class Test: X = MyDescriptor () 3. Customized sequence

Magic method:

_ _ len__ (self) _ _ getitem__ (self,key) _ _ setitem__ (self,key,value) _ _ delitem__ (self,key) _ _ iter__ (self) _ reversed__ (self) _ _ contains__ (self,item)

4. Iterator

For i in "FishC": print (I) FishC

A string is not only a container, but also an iterative object. The function of for statement is to trigger its iterative function, taking one data from the container one at a time, which is called iterative operation.

Python provides two BIF:iter () and next ().

Calling iter () on an iterable object gets its iterator, and calling next () iterator returns the next value.

String= "FishC" it=iter (string) next (it) 'F'next (it)' i'next (it) 's'next (it)' h'next (it) 'generator 5.

For calling a normal Python function, it usually starts with the first line of code of the function and ends with a return statement, an exception, or all statements.

two。 Exception handling 1. Exception type

(1) AssertionError: assertion statement (assert) failed.

My_list= ["Little Turtle"] assert len (my_list) > 0my_list.pop () 'Little Turtle' assert len (my_list) > 0Traceback (most recent call last): File "", line 1, in assert len (my_list) > 0AssertionError

(2) AttributeError: attempts to access unknown object properties.

My_list= [] my_list.fishcTraceback (most recent call last): File "", line 1, in my_list.fishcAttributeError: 'list' object has no attribute' fishc'

(3) IndexError: the index is out of range of the sequence.

My_list= [1 Traceback 2] my_list [3] Traceback (most recent call last): File "", line 1, in my_list [3] IndexError: list index out of range

(4) KeyError: look for a keyword that does not exist in the dictionary.

My_dict= {"one": 1, "two": 2} my_dict ["three"] Traceback (most recent call last): File ", line 1, in my_dict [" three "] KeyError: 'three'

(5) NameError: try to access a variable that does not exist.

FishcTraceback (most recent call last): File "", line 1, in fishcNameError: name 'fishc' is not defined

(6) OSError: an exception generated by the operating system.

(7) grammatical errors of SyntaxError:Python.

Print "I love fishc.com" SyntaxError: Missing parentheses in call to 'print'. Did you mean print (...)

(8) TypeError: invalid operation between different types.

1+'1'Traceback (most recent call last): File "", line 1, in 1+'1'TypeError: unsupported operand type (s) for +: 'int' and' str'

(9) ZeroDivisionError: divisor is zero.

5/0Traceback (most recent call last): File ", line 1, in 5/0ZeroDivisionError: division by zero2.try-except statement try: int ('abc') sum = 1 document 1' f = open ('I am a nonexistent document .txt') print (f.read ()) f.close () except (ValueError,TypeError) OSError) as reason: print ('error\ ncause of error is: + str (reason)') 3.try-finally statement try: F = open ('I am a nonexistent document .txt') print (f.read ()) sum=1+'1'except: print ('error') finally: f.close () 4.raise statement raise ZeroDivisionError5/0Traceback (most recent call last): File ", line 1, in 5/0ZeroDivisionError: division by zero5. Rich else statement try: int ('abc') except ValueError as reason: print (' error:'+ str (reason)) else: print ('nothing unusual!') try: with open ('data.txt' 'w') as f: for each_line in f: print (each_line) except OSError as reason: print (' error:'+ str (reason)) these are the magic methods and exception handling in the Python foundation shared by the editor. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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