不要为字典中没有值的键打印 None

Question

A dictionary was created with keys. Later some of the keys got values updated.

When printing the keys in a For loop, the keys without values, prints None.

ma_dict = dict.fromkeys(["David","Mike","Kate","Lilly"])
ma_dict.update({"David" : "Front", "Mike" : "Middle"})

for each in ["David","Mike","Kate","Lilly"]:
    print (each, ma_dict[each])

It prints:

David Front
Mike Middle
Kate None
Lilly None

What is the way not to print the None? Thank you.

# outputs wanted
David Front
Mike Middle
Kate 
Lilly 

Not to use an If statement, such as:

ma_dict = dict.fromkeys(["David","Mike","Kate","Lilly"])
ma_dict.update({"David" : "Front", "Mike" : "Middle"})

for each in ["David","Mike","Kate","Lilly"]:
    if ma_dict[each] != None:
        print (each, ma_dict[each])
    else:
        print (each)

Answer 1

If it's just for printing, you might consider using a dictionary comprehension to replace None with empty strings:

d = {k: ma_dict[k] if ma_dict[k] is not None else "" for k in ma_dict}
for k in d:
    print(k, d[k])
David Front
Mike Middle
Kate 
Lilly

Answer 2

Inspired by @masasa:

from collections import defaultdict

ma_dict = defaultdict(str)
ma_dict.update({"David" : "Front", "Mike" : "Middle"})

for each in ["David","Mike","Kate","Lilly"]:
    print (each, ma_dict[each])

It prints:

David Front
Mike Middle
Kate 
Lilly 

Answer 3

I think using if is appriopate here, but if you must Not to use an If statement AT ANY PRICE then do

ma_dict = dict.fromkeys(["David","Mike","Kate","Lilly"])
ma_dict.update({"David" : "Front", "Mike" : "Middle"})
for each in ["David","Mike","Kate","Lilly"]:
    print(each, [ma_dict[each],""][ma_dict[each] is None])

output

David Front
Mike Middle
Kate
Lilly

Answer 4

Since you don't want to use an if condition and As @masasa has suggested, You could use a defaultdict .

from collections import defaultdict
ma_dict = defaultdict.fromkeys(["David","Mike","Kate","Lilly"], '')
ma_dict.update({"David" : "Front", "Mike" : "Middle"})
for each in ["David","Mike","Kate","Lilly"]:
    print (each, ma_dict.get(each))

David Front
Mike Middle
Kate 
Lilly