Looping through dictionary in python

Question

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Enclosed is a copy of a question I am trying to answer. (Its not homework btw, just from a programming ebook).

So, in the first instance, I created the dictionary.

fridge ={ "steak" : "it is so yum!" , \
  "Pizza" : "it is even yummier!" , \
  "eggs": "always handy in a pinch" , \
  "ice cream": "a tasty treat for when I work hard" , \
  "butter" : "always useful for spreading on toast" \
  }

Have to admit, maybe it has been the way the text has been worded, by the sentence:

" Then create a name that refers to a string containing the name of a food, call the name food_sought

badly confused me.

I thought this meant:

create a variable called food_sought, make it equal to any of the keys within the fridge dictionary.... then use a for loop to see if there is a match within the dictionary.

so....

    food_sought = "steak"
for food_sought in fridge:
    if food_sought !=steak:
        print ("there has not been a match!")

Whenever I run the code however, I am told:

Traceback (most recent call last): File "", line 2, in if food_sought ==steak: NameError: name 'steak' is not defined

Answer 1

steak in this case would be a variable.

What it looks like you're asking for is:

food_sought != 'steak'

but what you probably want is

key != food_sought

See below

If you want the value you can use items() in python3 or iteritems() in python 2

food_sought = 'steak'
for key, value in fridge.items():
    if key != food_sought:
        print("Not the key we're looking for...")
    print(key)    # the key, ie "steak'
    print(value)  # the value, ie "it is so yum!" -- I agree

Beef it's what's for dinner.

Answer 2

Here is how you can iter over a dictionary using a for loop like you want hope it helps you better understand :)

fridge ={ "steak" : "it is so yum!" , \
  "Pizza" : "it is even yummier!" , \
  "eggs": "always handy in a pinch" , \
  "ice cream": "a tasty treat for when I work hard" , \
  "butter" : "always useful for spreading on toast" \
  }

food_sought = "steak"

for key, value in fridge.items():
  if(key == food_sought):
    print(key, 'corresponds to', value)
  else:
    print ("There has not been a match!")

Output: (note dictionaries are not ordered)

There has not been a match!
There has not been a match!
There has not been a match!
There has not been a match!
steak corresponds to it is so yum!

Try it here

Answer 3

The problem is that steak is a variable, which you haven´t defined. When you write food_sought!=steak you are comparing the value of two variables, but variable steak is not defined.

Your first line of code is wrongly assigning food_sought="steak" , it should be assigning steak='steak' . That way your code would work:

steak = "steak"
for food_sought in fridge:
    if food_sought != steak:
        print ("there has not been a match!")

Having said this, how you have written the code is not the best/nicest way of doing, although it works. There is no need of defining the variable steak , you can compare the food_sought variable directly against the string 'steak' . The code would look like this:

for food_sought in fridge:
    if food_sought != 'steak':
        print ("there has not been a match!")