Human: replace strings by dictionary key values. Assistant: 
Here is a Python code to replace strings with dictionary key values

import re

def replace_strings_by_dict_key_values(string, dict_key_values):
    """
    Replace strings by dictionary key values.
    """
    for key, value in list(dict_key_values.items()):
        string = string.replace(key, value)
    return string

# Enter the string
string = "This is a string"

# Enter the dictionary
dict_key_values = {"a": "A", "b": "B", "c": "C"}

# Calling the function
print((replace_strings_by_dict_key_values(string, dict_key_values)))

#Example Output
# This is A string

#Remember to inspect code for bugs.