Question

I was learning about dictionaries in Python and I created a simple program:

# Create an empty dictionary called d1
d1 = {}

# Print dictionary and length
def dixnary():
    print "Dictionary contents : "
    print d1
    print "Length = ", len(d1)

# Add items to dictionary
d1["to"] = "two"
d1["for"] = "four"

print "Dictionary contents :"
print d1
print "Length =" , len(d1)

# Print dictionary and length
print dixnary()

Now there’s a difference in the results when I use the print commands and when I use the dixnary function.

Using the print commands I get the result:

Dictionary contents:
<‘to’:’two’,’for:’four’>
Length = 2

and when I use the function dixnary, I get the results:

Dictionary contents:
<‘to’:’two’,’for:’four’>
Length = 2
None

Notice the None on the final line. This None gets added when I use the function dixnary. Why is this?

Answer 1

You’re attempting to print the return value of a function, but the function doesn’t return a value, so it returns the default value of None.

The reason why it prints out other data is that you have print commands inside of the function. Just run the function (dixnary()), instead of printing it (print dixnary()).

Or alternatively, have the program return the string, so you can do useful things with it.

def dixnary():
    return "Dictionary contents :\n%s\nLength = %d" % (d1, len(d1))

print dixnary()