如果这个变量不为None,那么条件variable_name is not None将返回True,否则返回False。 完整的代码示例 下面是一个完整的代码示例,展示了如何判断一个变量是否定义: defcheck_variable_defined(variable_name):ifvariable_nameinlocals()andlocals()[variable_name]isnotNone:print(f"{variable_name}已定义")else:prin...
下面是一个使用locals()函数判断变量是否已定义的示例代码: defcheck_variable_defined():variable_name='x'ifvariable_nameinlocals():print(variable_name,'is defined')else:print(variable_name,'is not defined')check_variable_defined() 1. 2. 3. 4. 5. 6. 7. 8. 以上代码中,我们定义了一个函数c...
Let’s first make a user-defined function named local_func(), it defines a variable and initializes the value in it. We can use the in operator to check if the string of the variable name exists in the dictionary. If so, it means the variable exists in the local namespace; otherwise...
Then it’s easy to test whether a variable is bound toNone: if x is None: some_fallback_operation( ) else: some_operation(x) Discussion Python doesn’t have a specific function to test whether a variable is defined, since all variables are expected to have been defined before use, even...
Checking local variable To check if a local variable exists or not, we can use the built-in locals() function. Example: def name(): a = "Hello" # a is a local variable if 'a' in locals(): print ('a variable exist') else: print ('a variable does not exist') name() Output:...
The int datatype is used to represent integers. In this tutorial, we will discuss how to check if a variable is int or not.In Python, we usually check the type() function to return the type of the object. For example,x = 10 print(type(x)) print(type(x) == int) ...
1 Why am I getting NameError: name 'array' is not defined 2 Error when running script with Spyder and Python(x,y)? 1 NameError: name 'first' is not defined 3 Why won't this variable reference to a non-local scope resolve? 0 the variable of the function in python ...
>>>ifFalse:...1+"two"# This line never runs, so no TypeError is raised...else:...1+2...3>>>1+"two"# Now this is type checked, and a TypeError is raisedTypeError:unsupportedoperandtype(s)for+:'int'and'str' 在第一个示例中,分支1 + "two"从不运行,因此永远不会经过类型检查。
We can use it to check if the variable is of type str. isinstance checks if a given object (first parameter) is: an instance of a class specified as a second parameter. For example, is variable an instance of the str class? or an instance of a subclass of a class specified as a...
在语法规则中,冒号左边的叫做非终结符(Non-terminal),又叫变元(Variable)。非终结符可以按照右边的正则表达式来逐步展开,直到最后都变成了标识符,字面量,运算符等这些不可展开的符号,就是终结符(Terminal),终结符其实就是词法分析中形成的Token 像这样左边是非终结符,右边是正则表达式的书写语法规则的方式,就叫做扩...