Aliyun Tianchi Python Training Camp (day3 check-in)

1. Overview of learning content

1.1 Learning address: Aliyun Tianchi python training camp

1.2 Mind map

2. Specific learning content

2.1 Exception handling

Anomalies are errors detected during runtime. The computer language defines exception types for possible errors. When a certain error causes a corresponding exception, the exception handler will be started to restore the normal operation of the program.

2.1.1 Summary of Python standard exceptions

• BaseException: All abnormal base class
• Exception: Conventional abnormality base class
• StandardError: The base class for all built-in standard exceptions
• ArithmeticError: The base class for all numerical calculation exceptions
• FloatingPointError: floating point calculation exception
• OverflowError : Numerical operation exceeds the maximum limit
• ZeroDivisionError : division by zero
• AssertionError : the assertion statement (assert) failed
• AttributeError : Attempt to access unknown object attribute
• EOFError: No built-in input, EOF mark reached
• EnvironmentError: The base class of operating system exceptions
• IOError: Input/output operation failed
• OSError : An exception generated by the operating system (for example, opening a file that does not exist)
• WindowsError: system call failed
• ImportError : When importing a module fails
• KeyboardInterrupt: user interrupt execution
• LookupError: The base class for invalid data query
• IndexError : The index is out of the range of the sequence
• KeyError : Find a keyword that does not exist in the dictionary
• MemoryError : memory overflow (memory can be released by deleting the object)
• NameError : Attempt to access a variable that does not exist
• UnboundLocalError: Access to uninitialized local variables
• ReferenceError: Weak reference attempts to access objects that have been garbage collected
• RuntimeError: General runtime exception
• NotImplementedError: Method not yet implemented
• SyntaxError : exception caused by syntax error
• IndentationError: exception caused by indentation error
• TabError: Tab and space are mixed
• SystemError: General interpreter system exception
• TypeError : invalid operation between different types
• ValueError : Invalid parameter passed
• UnicodeError: Unicode related exception
• UnicodeDecodeError: exception during Unicode decoding
• UnicodeEncodeError: exception caused by Unicode encoding error
• UnicodeTranslateError: exception caused by Unicode conversion error

There are hierarchical relationships within the exception system. Some relationships in the Python exception system are as follows:

---

2.1.2 Summary of Python standard warnings

• Warning: the base class for warnings
• DeprecationWarning: warning about deprecated features
• FutureWarning: A warning that the semantics of the structure will change in the future
• UserWarning: warning generated by user code
• PendingDeprecationWarning: A warning that the feature will be deprecated
• RuntimeWarning: warning of suspicious runtime behavior (runtime behavior)
• SyntaxWarning: Suspicious syntax warning
• ImportWarning: Used to trigger a warning during the import of a module
• UnicodeWarning: warnings related to Unicode
• BytesWarning: warnings related to bytes or bytecode
• ResourceWarning: warnings related to resource usage

2.1.3 try-except statement

try:
    检测范围
except Exception[as reason]:
    出现异常后的处理代码

The try statement works as follows:

• First, execute the tryclause ( the statement between the keyword tryand the keyword except)
• If no exception occurs, the exceptclause is ignored , and the tryclause ends after execution.
• If tryan exception occurs during the execution of the clause, the tryrest of the clause will be ignored. If the type of the exception exceptmatches the name after it, the corresponding exceptclause will be executed. try - exceptThe code after the last executed statement.
• If an exception does not match any except, then the exception will be passed to the upper layer try.

try:
    f = open('test.txt')
    print(f.read())
    f.close()
except OSError:
    print('打开文件出错')

# 打开文件出错

try:
    f = open('test.txt')
    print(f.read())
    f.close()
except OSError as error:
    print('打开文件出错\n原因是：' + str(error))

# 打开文件出错
# 原因是：[Errno 2] No such file or directory: 'test.txt'

A trystatement may contain multiple exceptclauses to handle different specific exceptions. Only one branch will be executed at most.

try:
    int("abc")
    s = 1 + '1'
    f = open('test.txt')
    print(f.read())
    f.close()
except OSError as error:
    print('打开文件出错\n原因是：' + str(error))
except TypeError as error:
    print('类型出错\n原因是：' + str(error))
except ValueError as error:
    print('数值出错\n原因是：' + str(error))

# 数值出错
# 原因是：invalid literal for int() with base 10: 'abc'

dict1 = {
    
    'a': 1, 'b': 2, 'v': 22}
try:
    x = dict1['y']
except LookupError:
    print('查询错误')
except KeyError:
    print('键错误')
else:
    print(x)

# 查询错误

try-except-elseThe statement tried to query dicta key-value pair that was not in, which caused an exception. This exception should belong to exactly KeyError, but because it KeyErroris LookupErrora subclass and will be LookupErrorplaced KeyErrorbefore it, the program executes the exceptcode block first. Therefore, when using multiple exceptcode blocks, you must adhere to the order of their specifications, from the most targeted exception to the most general exception.

dict1 = {
    
    'a': 1, 'b': 2, 'v': 22}
try:
    x = dict1['y']
except KeyError:
    print('键错误')
except LookupError:
    print('查询错误')
else:
    print(x)

# 键错误

A exceptclause can handle multiple exceptions that will be placed in a parenthesis as a tuple.

try:
    s = 1 + '1'
    int("abc")
    f = open('test.txt')
    print(f.read())
    f.close()
except (OSError, TypeError, ValueError) as error:
    print('出错了！\n原因是：' + str(error))

# 出错了！
# 原因是：unsupported operand type(s) for +: 'int' and 'str'

2.1.4 try-except-finally statement

try:
detection range
except Exception[as reason]:
processing code after an exception
finally: code that
will be executed anyway

Regardless of whether tryan exception occurs in the finallyclause , the clause will be executed.

If an exception tryis thrown in the clause without any exceptinterception, then the exception will be finallythrown after the clause is executed.

def divide(x, y):
    try:
        result = x / y
        print("result is", result)
    except ZeroDivisionError:
        print("division by zero!")
    finally:
        print("executing finally clause")


divide(2, 1)
# result is 2.0
# executing finally clause
divide(2, 0)
# division by zero!
# executing finally clause
divide("2", "1")
# executing finally clause
# TypeError: unsupported operand type(s) for /: 'str' and 'str'

2.1.5 try-except-else statement

If tryno exception occurs during the execution of the clause, Python will execute the elsestatement following the statement.

try:
    检测范围
except:
    出现异常后的处理代码
else:
    如果没有异常执行这块代码

exceptIt is not a good way to use it without any exception type. We cannot identify specific exception information through this program, because it catches all exceptions.

try:
detection range
except(Exception1[, Exception2[,...ExceptionN]]]):
if one of the above exceptions occurs, execute this code
else:
if there is no exception, execute this code

try:
    fh = open("testfile.txt", "w")
    fh.write("这是一个测试文件，用于测试异常!!")
except IOError:
    print("Error: 没有找到文件或读取文件失败")
else:
    print("内容写入文件成功")
    fh.close()

# 内容写入文件成功

Note: elseThe existence of a exceptstatement must be based on the existence of exceptthe trystatement. Using a statement in a elsestatement without a statement will cause a grammatical error.

2.1.6 raise statement

Python uses the raisestatement to throw a specified exception.

try:
    raise NameError('HiThere')
except NameError:
    print('An exception flew by!')
    
# An exception flew by!

Three, study summary

I have only learned the try-except statement for the exception handling I encountered before, and I am not familiar with the various exception prompts encountered. I guess the meaning according to the English guess. After learning today, I have a deeper understanding of various exceptions and methods to handle exceptions. And more.

Today’s content is quite important. I’m not familiar with it before. The opening is completed on the third day. Come on (◍°∇°◍)ﾉﾞ