Python中的参考语义混乱

Question

I'm trying to drop missing values from two Pandas dataframes:

Data1 = pd.read_csv(r"C:\Users\Zihao\Desktop\New\OBSTET.csv")

Data2 = pd.read_csv(r"C:\Users\Zihao\Desktop\New\PRODUCTOS.csv", index_col = 0)

def DropNan(Data1, Data2):
    Data1 = Data1.dropna()
    Data2 = Data2.dropna()

When I cal the method, it is not working (it doesn't drop the missing values). I wonder what caused this problem?

My guess is that it related to reference semantics in Python I do not understand. Could someone explain?

Answer 1

In your function, Data1 and Data2 are parameters, and therefore local variables. The fact that they happen to have the same name as your global variables is irrelevant (except in causing some extra confusion).

If you want to change the global variables, do it like this:

def DropNan():
    global Data1, Data2
    Data1 = Data1.dropna()
    Data2 = Data2.dropna()

DropNan()

Or, if you want to take these two values as parameters, you almost certainly want to return two values:

def DropNan(d1, d2):
    return d1.dropna(), d2.dropna()

Data1, Data2 = DropNan(Data1, Data2)