Python - Replacing words in a string with entries from a dictionary

Question

I am trying to make a program that will take an input, look to see if any of these words are a key in a previously defined dictionary, and then replace any found words with their entries. The hard bit is the "looking to see if words are keys". For example, if I'm trying to replace the entries in this dictionary:

dictionary = {"hello": "foo", "world": "bar"}

how can I make it print "foo bar" when given an input "hello world"?

Solution 1

Different approach

def replace_words(s, words):
    for k, v in words.iteritems():
        s = s.replace(k, v)
    return s

s = 'hello world'
dictionary = {"hello": "foo", "world": "bar"}

print replace_words(s, dictionary)

Solution 2

The cleanest method is to use dict.get to fallback to the word itself if the word is not in the dictionary:

' '.join([dictionary.get(word,word) for word in 'hello world'.split()])

Solution 3

This works in Python 2.x:

dictionary = {"hello": "foo", "world": "bar"}
inp = raw_input(":")
for key in inp.split():
    try:
        print dictionary[key],
    except KeyError:
        continue

However, if you are on Python 3.x, you will want this:

dictionary = {"hello": "foo", "world": "bar"}
inp = input(":")
for key in inp.split():
    try:
        print(dictionary[key], end="")
    except KeyError:
        continue

Comments

[Admin]

Tip: Whenever you use str.join, use a list comprehension over a generator expression. Reference: stackoverflow.com/a/9061024/2555451

[roippi]

@iCodez yeah, I always forget that one. Thanks.

[wakkydude]

Can you use "k" and "v" anywhere in python to represent keys and values? If not, where in this code is it defined that k is a key and v is a value for dictionaries?

[Wooble]

@wakkydude the "for k, v in ..." bit unpacks the tuples returned by iteritems() into those names. You can call them anything you want, but k and v are typical names.

[Guy Markman]

In python 3, it's words.items() instead of words.iteritems()