Why there are some print when the functin is not called in flask?

Question

The following code （pseudocode） in flask confused me a lot.

def IsIllegal(f):
    @wraps(f)
    def decorated(*args,**kwargs):
        if True:
            return error msg
        else:
            return f(*args,**kwargs)
    return decorated

@IsIllegal
@app.route(...,  methods = ['POST']  )
def func1():
    data = flask.request.get_data()
    print(data)
    ...

where function IsIllegal is used to check if the user is NOT logged in. What I found is that func1 always print the data even the user is not logged in. The return value of func1 is, as expected, stopped by the function IsIllegal. But I feel that it is not save because the statement in func1 is executed (the print). How can I understand this?

Can you make sure that you post **valid Python**? `return error msg` is not valid. — Martijn Pieters, Oct 16 '18 at 12:18

score 0 · Accepted Answer · answered Oct 16 '18 at 12:19

You registered the undecorated func1() function. The @IsIllegal() decorator result is applied after registration by the @app.route() decorator, and is never called when the route is accessed.

Decorators are applied in reverse order, from the inside out, so to speak. Reverse the decorators:

@app.route(...,  methods = ['POST']  )
@IsIllegal
def func1():

Now the result of IsIllegal(func1) is registered by @app.route(...), so accessing the route will end up calling decorated().

Why there are some print when the functin is not called in flask?

1 Answers1