Confused on dictionary input example in Python Crash Course
Question:
I am working my way through Python Crash Course, and in Chapter 8 the author gives the following code as an example for filling a dictionary with user input. I am confused in the step where he stores the responses into the dictionary, as to my eye it looks as though he is only saving one piece of , "response" which is immutable data to the "responses" dictionary under the key "name". I am missing how both the name input and response input are put into the dictionary.
It seems to make no sense to me, but that is what I have loved about this journey so far, finding sense in seeming nonsense. Thank you for helping demystify this world for me.
responses = {}
# Set a flag to indicate that polling is active.
polling_active = True
while polling_active:
#Prompt for the person's name and response.
name = input("nWhat is your name? ")
response = input("Which mountain would you like to climb someday? ")
#Store the response in the dictionary:
responses[name] = response
#Find out if anyone else is going to take the poll.
repeat = input("Would you like to let another person respond? (yes/no) ")
if repeat == 'no':
polling_active = False
#Polling is complete. Show the results.
print("n--- Poll Results ---")
for name, response in responses.items():
print(name + " would like to climb " + response + ".")
Answers:
In the most basic explanation, dictionaries associates an arbitrary value at an arbitrary key. So, what the author is actually doing is associating the user’s response with their name. The author does this by using the name as a key and the response as a value. Using dictionaries like this is fairly common.
If you want to retrieve a value in the array, you must know it key. However, you can retrieve all key and value pairs with dictionary.items(). This way, the author can get those two associated pieces of data (the name and the response).
The thing with dictionaries is that you can change the value of the key like this: dictionary[key] = value. If the key doesn’t exist it will simply create a new key. You don’t need any function like append which is used for lists. The line where you wrote responses[name] = response works because it stays in a while loop. After the loop runs again it asks another input and replaces the old name with a new name and old response with a new response. In conclusion, name and response is added every time the loop runs if the name is not already in the dictionary. If the name is there then it will simply change its value response if that is different from the old one.
Does this answer your question?
name and response are variables names that are filled with the inputted data, let’s say 'John' and 'Kalimanjaro'.
Now, 'John' and 'Kalimanjaro' are indeed immutable, but that doesn’t mean you can’t replace the values stored in name and response in the next loop. You can assign a new value, maybe also immutable, to name if you want.
One possible source of confusion could be that you started learning dictionaries using statements like responses['John'] = 'Kalimanjaro', where both key and value were strings. Now you are doing responses[name] = response (no quotes around name and response). So you create a key called whatever was stored in name and a value with whatever was stored in response.
If in the next iteration the value of name is replaced by, let’s say 'Maria' and response becomes 'Andes', the new responses[name] = response will be equivalent to responses['Maria'] = 'Andes'.
I am working my way through Python Crash Course, and in Chapter 8 the author gives the following code as an example for filling a dictionary with user input. I am confused in the step where he stores the responses into the dictionary, as to my eye it looks as though he is only saving one piece of , "response" which is immutable data to the "responses" dictionary under the key "name". I am missing how both the name input and response input are put into the dictionary.
It seems to make no sense to me, but that is what I have loved about this journey so far, finding sense in seeming nonsense. Thank you for helping demystify this world for me.
responses = {}
# Set a flag to indicate that polling is active.
polling_active = True
while polling_active:
#Prompt for the person's name and response.
name = input("nWhat is your name? ")
response = input("Which mountain would you like to climb someday? ")
#Store the response in the dictionary:
responses[name] = response
#Find out if anyone else is going to take the poll.
repeat = input("Would you like to let another person respond? (yes/no) ")
if repeat == 'no':
polling_active = False
#Polling is complete. Show the results.
print("n--- Poll Results ---")
for name, response in responses.items():
print(name + " would like to climb " + response + ".")
In the most basic explanation, dictionaries associates an arbitrary value at an arbitrary key. So, what the author is actually doing is associating the user’s response with their name. The author does this by using the name as a key and the response as a value. Using dictionaries like this is fairly common.
If you want to retrieve a value in the array, you must know it key. However, you can retrieve all key and value pairs with dictionary.items(). This way, the author can get those two associated pieces of data (the name and the response).
The thing with dictionaries is that you can change the value of the key like this: dictionary[key] = value. If the key doesn’t exist it will simply create a new key. You don’t need any function like append which is used for lists. The line where you wrote responses[name] = response works because it stays in a while loop. After the loop runs again it asks another input and replaces the old name with a new name and old response with a new response. In conclusion, name and response is added every time the loop runs if the name is not already in the dictionary. If the name is there then it will simply change its value response if that is different from the old one.
Does this answer your question?
name and response are variables names that are filled with the inputted data, let’s say 'John' and 'Kalimanjaro'.
Now, 'John' and 'Kalimanjaro' are indeed immutable, but that doesn’t mean you can’t replace the values stored in name and response in the next loop. You can assign a new value, maybe also immutable, to name if you want.
One possible source of confusion could be that you started learning dictionaries using statements like responses['John'] = 'Kalimanjaro', where both key and value were strings. Now you are doing responses[name] = response (no quotes around name and response). So you create a key called whatever was stored in name and a value with whatever was stored in response.
If in the next iteration the value of name is replaced by, let’s say 'Maria' and response becomes 'Andes', the new responses[name] = response will be equivalent to responses['Maria'] = 'Andes'.