In my introduction to python course we were covering the input function last time and I saw that whatever you type as an input is stored as a string. You can use the int() and float() before the input function to store as a number but I was wondering how can it be used to store a function the user enters. Is there a way to use input to allow me to define a function?
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- Welcome! I think you would benefit from taking a look at this article: thepythonguru.com/python-builtin-functions/evalbracco23– bracco232019-04-08 12:49:45 +00:00Commented Apr 8, 2019 at 12:49
- 3This is nearly always a bad idea- if you're writing the input then you can easily edit the source. If another 'user' is writing the input then they can easily write malicious code that you will then execute. I suggest take the string input and parse it carefully to only validate the kinds of input you wantChris_Rands– Chris_Rands2019-04-08 13:00:05 +00:00Commented Apr 8, 2019 at 13:00
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3 Answers
You can do this using the exec() built in function.
https://docs.python.org/3/library/functions.html#exec
my_function_def = ''' def my_function(): print('Greetings from my function!') ''' exec(my_function_def) my_function() # -> 'Greetings from my function!' 
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One potential solution is to allow the user to call a pre-defined method by name. This is more secure than using the exec() command outright, as it strictly limits the user's ability to trigger code blocks.
def SomeAction(): print("SomeAction has been executed.") userInput = input("Enter method name: ") if(userInput == SomeAction.__name__): method = getattr(sys.modules[__name__], SomeAction.__name__) #Get method by name method() However, if you're talking about having the user define a method completely from input calls, then you'll need to create an input loop to get the method body.
print("Enter your method declaration: ") methodDeclaration = "" methodLine = "X" i = 1 while(len(methodLine) != 0): methodLine = input(str(i) + ": ") i = i+1 methodDeclaration = methodDeclaration +"\n"+ methodLine print("Method to be executed:") print(methodDeclaration) exec(methodDeclaration) myMethod() The output of the above code is as below:
Enter method name: SomeAction SomeAction has been executed. Enter your method declaration: 1: def myMethod(): 2: print("MyMethod is running!") 3: Method to be executed: def myMethod(): print("MyMethod is running!") MyMethod is running! Be advised that this is not a secure practice. Using exec() allows the user to input any desired command into your python script. That being said, it is indeed possible to have user-defined methods from input.
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def A(arg): """function definations """ return arg def B(func): """ function defination B with func as argument """ return func(input()) B(A) more ref: Python function as a function argument?
