How to make composite dictionary from several other dicts [duplicate]

I have two dictionaries. I want to have a third which contains every key/value pair of dict a and dict b, if there is a key:value pair in dict b which has the same key as a key:value pair in dict a then i want to use the key:value pair in dict b. If there is a key:value pair in b which is not in dict a i want the output dict to also contain that key:value pair. I thought “if key in a” would be a way to check if a key from dict b exists in dict a but for some reason it always seems to be true (which i don’t think is the case).

Code

a = {"bill": 22, "ben": 21}

b = {"bez": 38, "ben": 55}
    
d = {}

for k,v in a.items():
      print("\n")
      print("when a[k] is ", str(k))
      for key,val in b.items():
          print("_b key is ",str(key))
          if key in a:
              print("______ k is in a", str(a[k]))
          
          
          
          

Desired output

d = {"bill": 22,
    "bez": 38,
    "ben": 55}