CODEWITHSUNDEEP
pythonpython-2.7dictionary
Minh Truong
Minh Truong

Reputation: 3

Learn Python The Hard Way Ex40

I'm learning python from the book called "Learn python the hard way" and i came across this block of code in exercise40

cities = {'CA': 'San Francisco', 'MI': 'Detroit', 'FL': 'Jacksonville'}

cities['NY'] = 'New York'
cities['OR'] = 'Portland'

def find_city(themap, state):
    if state in themap:
        return themap[state]
    else:
        return "Not found."

# ok pay attention!
cities['_find'] = find_city

while True:
    print "State? (ENTER to quit)",
    state = raw_input("> ")
    if not state: break

# this line is the most important ever! study!
city_found = cities['_find'](cities, state)
print city_found

1.Is it necessary to add "find_city" function to the dictionary?

2.Can i remove "themap" argument in the function "find_city"?

Here is my new code and it can still run without any error:

cities = {"CA" : "San Francisco", "MI" : "Detroit", "FL" : "Jacksonville"}

cities["NY"]= "New York"
cities["OR"] = "Portland"

def find_city(state):
    if state in cities:
        return cities[state]
    else:
        return "Not Found."

while True:
    print "State? (ENTER to quit)",
    state = raw_input(">")
    if not state:
        break
    city_found = find_city(state)
    print city_found

Upvotes: 0

Views: 285

Answers (3)

Patrick Artner
Patrick Artner

Reputation: 51663

You can do this, but the first 'codepiece' example stores a "functionpointer" for the find-function inside the dictionary itself so you can use the function by using a key of '_find' and supply the parameters to the found value (the FP) for this key.

I do not know the book, but probably this is done on a purpose, like f.e. to teach you that "values" in a dictionary can be of different types - maybe even an introduction to study functions as objects and how to use them....

In a real world example I would not do this, I might wrap the whole dictionary in a class and supply class methods IF (and thats a big if) there are other concerns that leads me to wrap stuff for this class...

All in all it is a very contreived example (in germany we would say "An den Haaren herbeigezogen" wich roughly translates to "pulled by it's hairs" (word by word) or "pulled out of the a..")

I think you are better of using the python3 website and its examples to learn - there are plenty of things to gain there - and study the documentation.

Start here: https://docs.python.org/3/tutorial/

Upvotes: 1

Daniel
Daniel

Reputation: 42758

Yes, it's strange, to put a function in a dictionary with cities. I wouldn't do that, but I don't know, what the author want to demonstrate with.

It is not a good idea, to rely on the global variable cities in find_city.

Usually, you would use .get:

def find_city(mapping, state):
    return mapping.get(state, "Not Found.")

while True:
    print "State? (ENTER to quit)",
    state = raw_input(">")
    if not state:
        break
    city_found = find_city(cities, state)
    print city_found

Upvotes: 3

Antti Haapala -- Слава Україні
Antti Haapala -- Слава Україні

Reputation: 133929

  1. no, it is not.

  2. yes you can.

And as a side note, many of the top answerers here on Stack Overflow do not recommend using Learn Python the Hard Way - quite contrary. As a newcomer, in 2017, your time would be more well-spent learning Python 3 and using some other resource.

Upvotes: 5

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