mapping_three_ways.py

# your function works on a single element in your container
def converter(period):
    period = period.lower()
    if period[-1:] == "d":
        period_unit = 1
    elif period[-1:] == "w":
        period_unit = 7
    elif period[-1:] == "m":
        period_unit = 30
    elif period[-1:] == "y":
        period_unit = 360
    else:
        print(period)
        raise Exception("Period not recognized!")

    return 10*period_unit

# here we use a list
period_list = ['1D', '1W', '1M', '1Y']

# most basic way: for-loop
new_list = []
for p in period_list:
    new_list.append(converter(p))
print(new_list)

# using a list-comprehension that is equivalent
# to the above for-loop
new_list2 = [converter(p) for p in period_list]
print(new_list2)

# using map
new_list3 = list(map(converter, period_list))
print(new_list3)