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This article introduces the knowledge of "what is the method of Python permanent storage and exception handling". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Permanent storage of Python (pickle module)

Stored as a binary sequence

Storage: pickling

Reading: unpickling

Permanently store a list

> import pickle

> my_list = [123 another list' 3.14159, ['Chinese]]

> pickle_file = open ('E:\ hyx02\ Python Learning\ my_list.pkl','wb')

> pickle.dump (my_list,pickle_file)

> pickle_file.close

You can write anything with a suffix in my_list.pkl.

The dump () method above:

Pickle.dump (obj, file, [, protocol])

Serialize the object and save the object obj to the file file. The parameter protocol is serialized, and the default is 0 (ASCII protocol, which means serialized as text), and the values of protocol can also be 1 and 2 (1 and 2 means serialized in binary form. Where 1 is the old binary protocol; 2 is the new binary protocol. File represents the class file object saved to. File must have a write () interface. File can be a file opened with'w' or a StringIO object, or any object that can implement the write () interface.

Test the stored results just now:

> pickle_file = open ('E:\ hyx02\ Python Learning\ my_list.pkl','rb')

> my_list2 = pickle.load (pickle_file)

> print (my_list2)

[123,3.14159, 'China', [' another list']]

Rb in code: binary form

By the same token:

Permanently store a dictionary

We can use this method to turn the data into a packet.

For example, write a dictionary (information about many cities) as a package

> import pickle

> pickle_file=open ('E:\ hyx02\ Python Learning\ city_data.aaa','wb')

City= {'Beijing': abbreviated as "Beijing", known as Yanjing and Peiping in ancient times, is the capital, provincial administrative region, municipality directly under the Central Government, national central city and mega-city of the people's Republic of China.' }

> pickle.dump (city,pickle_file)

> > pickle_file.close ()

Then when it is called:

> import pickle

> pickle_file=open ('E:\ hyx02\ Python Learning\ city_data.aaa','rb')

> city2 = pickle.load (pickle_file)

> city2

{'Beijing': abbreviated as "Beijing", formerly known as Yanjing and Peiping, is the capital, provincial administrative region, municipality directly under the Central Government, national central city and mega-city of the people's Republic of China.' }

The procedure can be streamlined.

Exception handling of Python (Exception)

File_name = input ('Please enter the file name you want to open:')

F = open (file_name)

Print ('contents of the file are:')

For each_line in f:

Print (each_line)

Enter the wrong file name: throw the file exception FileNotFoundError not found

FileNotFoundError: [Errno 2] No such file or directory: 'aaa'

Common anomalies

AssertionError: assertion statement (assert) failed

> my_list = ['aaaaa']

> assert len (my_list) > 0

> > my_list.pop ()

'aaaaa'

> assert len (my_list) > 0

Traceback (most recent call last):

File "", line 1, in

Assert len (my_list) > 0

AssertionError

An AssertionError exception is thrown and assert is used as a checkpoint in the middle of the program

As shown below:

AttributeError: attempt to access unknown object properties

> my_list.aaa

Traceback (most recent call last):

File "", line 1, in

My_list.aaa

AttributeError: 'list' object has no attribute' aaa'

An AttributeError exception is thrown, as shown below:

IndexError: the index is out of range of the sequence

KeyError: Key that does not exist

> my_dict = {'one':1,'two':2,'three':3}

> my_dict ['fout']

Traceback (most recent call last):

File "", line 1, in

My_dict ['fout']

KeyError: 'fout'

A KeyError exception is thrown, as shown below:

# using the get () method will not throw an exception

NameError: accessing variables that do not exist

OSError: there are many exceptions generated by the operating system. For example, the original FileNotFoundError belongs to OSError.

OverflowError: numeric operations exceed the maximum limit, which is not common in Python

Syntax error of SyntaxError:Python

> > print 'aaa'

SyntaxError: Missing parentheses in call to 'print'. Did you mean print ('aaa')?

Throw a syntax error without parentheses and change it into the form of a function call

As shown below:

Which Zhengzhou abortion hospital has a good http://3g.zyfuke.com/?

TypeError: cannot be calculated, for example, operations between different types

ZeroDivisionError: divisor 0

Anomaly detection

Try_except statement

Try:

Detection range

Except Exception [as reason]:

Handling code after an exception (Exception) occurs

Example:

Try:

F = open ('xxx.txt')

Print (f.read ())

F.close ()

Except OSError as reason:

Print ('file error ~\ nThe reason for the error is:' + str (reason))

Except TypeError as reason:

Print ('type error ~\ nThe reason for the error is:' + str (reason))

The running result is as follows:

Try:

Sum = 1 +'1'

F = open ('xxx.txt')

Print (f.read ())

F.close ()

Except OSError as reason:

Print ('file error ~\ nThe reason for the error is:' + str (reason))

Except TypeError as reason:

Print ('type error ~\ nThe reason for the error is:' + str (reason))

The running result is as follows:

You can also merge writing:

Except (OSError,TypeError) as reason:

Print ('error ~\ nThe reason for the error is:' + str (reason))

However, the above try_except statement is not recommended, for example, the file is not closed due to program interruption, so there are: try-finally statement

Try-finally statement

Try:

Detection range

Except Exception [as reason]

Handling code after an exception (Exception) occurs

Finally:

Code that will be executed anyway

Example:

Try:

F = open ('xxx.txt')

Print (f.read ())

Sum = 1 +'1'

Except (OSError,TypeError) as reason:

Print ('error ~\ nThe reason for the error is:' + str (reason))

Finally:

F.close ()

Raise statement

> raise ZeroDivisionError ('exception with divisor 0')

Show the above explanation

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