Switch-case like structure in python

Question

I have the following function that I've made which takes a member's sign-in date and the length of their contract and returns a modified dataframe with an expiration date for each member. The function works as intended, but I wanted to know if there was a cleaner way of writing the nested function month_to_num(ind). I know python does not implement cases, but is there a way to rewrite the all the if/elif/else statements?

def renewal_date(df):

    def month_to_num(ind):
        if (df.loc[ind, "Contract Type"] == "1 Month"):
            return 1
        elif (df.loc[ind, "Contract Type"] == "3 Months Prom" or 
              df.loc[ind, "Contract Type"] == "3 Month"):
            return 3
        elif (df.loc[ind, "Contract Type"] == "4 Month Promo"):
            return 4
        elif (df.loc[ind, "Contract Type"] == "6 Months"):
            return 6
        else:
            return 12

    for z in range(0, len(df)): 
        exp_date = (df.loc[z, "Date-Joined"] + 
                    relativedelta(months=+month_to_num(z)))
        df.set_value(z,"Date-Renewal", exp_date)

    return df

You can typically use python dictionaries to replace `case` statements or large `if/elif` blocks. — Brendan Abel, Apr 26 '16 at 20:00

score 3 · Accepted Answer · edited Apr 13 '17 at 12:40

3

This is more suited to the Code Review Stack Exchange, but to preserve functionality, you'd ordinarily use a dictionary:

MONTH_NUMS = {
    '1 Month': 1,
    '3 Months Prom': 3,
    '3 Month': 3,
    '4 Month Promo': 4,
    '6 Months': 6,
}

def month_to_num(ind):
    return MONTH_NUMS.get(df.loc[ind, 'Contract Type'], 12)

That said, there's a bit of a code smell here in how we are mapping strings to numbers this way.

edited Apr 13 '17 at 12:40

Community

1
1

answered Apr 26 '16 at 20:01

Dietrich Epp

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Thank you, I was unaware that place existed – Lukasz Apr 26 '16 at 20:05

score 2 · Answer 2 · answered Apr 26 '16 at 20:01

You can use a dictionnary in coordination with the dict.get() method which return a default value if the key doesn't exists in the dictionnary.

def renewal_date(df):
    def month_to_num(ind):
        contract_types = {'1 Month': 1, '3 Months Prom': 3, '4 Month Promo': 4, '6 Months': 6}

        return contract_types.get(df.loc[ind, "Contract Type"], 12)

    for z in range(0, len(df)):
        exp_date = (df.loc[z, "Date-Joined"] +
                    relativedelta(months=+month_to_num(z)))
        df.set_value(z, "Date-Renewal", exp_date)

    return df

Switch-case like structure in python

2 Answers2