How to solve the invalid calling parameter error of Python?

Python is a high-level programming language that is widely used in scientific computing, data analysis, automation, web development and other fields. In Python application development, the error of illegal calling parameters is a common programming error, which may cause the program to crash or the running results to be inconsistent with expectations. This article will introduce the causes of illegal calling parameters in Python and how to solve this error.

1. How to call parameters in Python

In Python, there are two ways to call functions and methods:

1. Positional parameter calling method

Positional parameters refer to parameters that are passed in the order in which they are defined. For example, the following function definition has two positional parameters a and b:

def add(a, b):
    return a + b

When calling the function, you can pass the parameters in the order of the positional parameters:

result = add(1, 2)

Here 1 and 2 are assigned to the parameters respectively. a and b, the function returns 3.

2. Keyword parameter calling method

Keyword parameters are parameters passed according to the parameter name. For example, the following function definition has two keyword parameters x and y:

def sub(x, y):
    return x - y

When calling the function, you can pass the parameters by specifying the parameter name:

result = sub(x=3, y=1)

Here 3 and 1 are assigned to the parameters respectively. x and y, the function returns 2.

2. Causes of illegal Python call parameter errors

Illegal Python call parameter errors usually have the following reasons:

1. The number of parameters does not match

When a function or method is called and the number of parameters passed does not match the number of parameters defined, an illegal parameter error occurs. For example, the following function definition has two positional parameters a and b, but only one parameter is passed when calling:

def add(a, b):
    return a + b

result = add(1)

Only one parameter 1 is passed here, but the function definition requires two positional parameters, so it will An illegal parameter error occurred.

2. Mixing positional parameters and keyword parameters

When positional parameters and keyword parameters are mixed, parameter mismatch may occur. For example, the following function definition has two positional parameters a and b and a keyword parameter c:

def func(a, b, c=0):
    return a + b + c

When calling the function, you can pass a value to the keyword parameter c by specifying the parameter name:

result = func(1, 2, c=3)

You can also use positional parameters to pass parameter values:

result = func(1, 2, 3)

However, if you use the keyword parameter c to pass the positional parameter, an illegal parameter error will occur:

result = func(1, 2, c=4, 5)

Use both here Keyword parameters and positional parameters are omitted, resulting in parameter mismatch.

3. Passing illegal type parameters

When the passed parameter type is inconsistent with the parameter type defined by the function or method, an illegal parameter error will also occur. For example, the following function definition requires an integer parameter:

def func(num):
    return num * 2

But when a string parameter is passed, an illegal parameter error occurs:

result = func('hello')

The string type passed here parameter, but the function definition requires an integer type parameter.

3. How to solve the illegal error of Python calling parameters

When an illegal Python parameter error occurs, common solutions include the following:

1. Check the parameters Number and type

First you need to check whether the number and type of parameters passed when calling the function or method are consistent with the number and type of parameters defined by the function or method. For example, the following code checks whether the number of parameters passed when calling the function is correct:

def func(a, b, c):
    pass

args = (1, 2, 3)
if len(args) != 3:
    print('参数数量不正确')
else:
    func(*args)

Here uses the tuple args to store the passed parameters, and then checks whether the length of args is equal to 3. If not, it will prompt that the number of parameters is incorrect. , otherwise the func function is called.

2. Use keyword parameters

Using keyword parameters can avoid the problem of incorrect parameter order and can also improve the readability of the code. For example, the following code uses keyword parameters to call a function:

def func(a, b, c):
    pass

params = {'a': 1, 'b': 2, 'c': 3}
func(**params)

Here, the dictionary params is used to store the parameters passed when the function is called, and then **params is used to unpack the parameters in params and pass them to the function.

3. Set default values

Setting default values ​​for parameters of a function or method can make it more flexible when called. For example, the following function definition sets a default parameter value:

def func(a, b=0, c=0):
    pass

When calling the function, you can pass only one parameter a, or you can pass both b and c at the same time:

func(1)              # 只传递a参数，b和c使用默认值0
func(1, 2, 3)        # 传递a、b和c参数
func(a=1, c=3)       # 使用关键字参数传递a和c参数，b使用默认值0

Here b and The default value of c is 0. If no parameters are passed, the default value is used.

4. Catch exception

When an illegal Python parameter error occurs, the program may crash or output an error message. To avoid this situation, exceptions can be caught and handled in the program. For example, in the following code, a try-except statement is used to catch exceptions with illegal parameters:

def func(a, b):
    pass

try:
    result = func(1)
except TypeError:
    print('参数不合法')

Only one parameter is passed when calling the func function, but the function definition requires two parameters, so parameter inconsistencies will occur. Legal error. Use the try-except statement to catch and handle this exception and output prompt information.

In summary, Python's illegal calling parameters errors may affect the running results and performance of the program, but this error can be avoided by using appropriate methods. In daily programming, you need to carefully check the number, type, and default value of parameters of a function or method, and avoid using mixed parameter passing methods. At the same time, for inevitable exceptions, try-except statements need to be used to catch errors and handle exceptions.

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