(Python基础教程之六)Python中的关键字
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Python关键字是python编程语言的保留字。这些关键字不能用于其他目的。
Python中有35个关键字-下面列出了它们的用法。
Keyword | Description | ||
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and | A logical AND operator. Return True if both statements are True .
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or | A logical OR operator. Returns True if either of two statements is true. If both statements are false, the returns False .
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as | It is used to create an alias.
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assert | It can be used for debugging the code. It tests a condition and returns True , if not, the program will raise an AssertionError.
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async | It is used to declare a function as a coroutine, much like what the @asyncio.coroutine decorator does.
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await | It is used to call async coroutine.
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class | It is used to create a class.
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def | It is used to create or define a function.
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del | It is used to delete objects. In Python everything is an object, so the del keyword can also be used to delete variables, lists, or parts of a list, etc.
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if | It is used to create conditional statements that allows us to execute a block of code only if a condition is True .
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elif | It is used in conditional statements and is short for else if .
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else | It decides what to do if the condition is False in if..else statement.
It can also be use in
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try | It defines a block of code ot test if it contains any errors. | ||
except | It defines a block of code to run if the try block raises an error.
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finally | It defines a code block which will be executed no matter if the try block raises an error or not.
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raise | It is used to raise an exception, manually.
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False | It is a Boolean value and same as 0. | ||
True | It is a Boolean value and same as 1. | ||
for | It is used to create a for loop. A for loop can be used to iterate through a sequence, like a list, tuple, etc.
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while | It is used to create a while loop. The loop continues until the conditional statement is false.
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break | It is used to break out a for loop, or a while loop.
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continue | It is used to end the current iteration in a for loop (or a while loop), and continues to the next iteration.
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import | It is used to import modules.
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from | It is used to import only a specified section from a module.
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global | It is used to create global variables from a no-global scope, e.g. inside a function.
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in | 1. It is used to check if a value is present in a sequence (list, range, string etc.). 2. It is also used to iterate through a sequence in a for loop.
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is | It is used to test if two variables refer to the same object.
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lambda | It is used to create small anonymous functions. They can take any number of arguments, but can only have one expression.
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None | It is used to define a null value, or no value at all. None is not the same as 0, False, or an empty string.None is a datatype of its own (NoneType) and only None can be None.
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nonlocal | It is used to declare that a variable is not local. It is used to work with variables inside nested functions, where the variable should not belong to the inner function.
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not | It is a logical operator and reverses the value of True or False.
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pass | It is used as a placeholder for future code. When the pass statement is executed, nothing happens, but you avoid getting an error when an empty code is not allowed.
Empty code is not allowed in loops, function definitions, class definitions, or in if statements.
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return | It is to exit a function and return a value.
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with | Used to simplify exception handling | ||
yield | To end a function, returns a generator |
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