Use format to print list that can contain an unknown number of variables at run time?

Question

The following works when I know that sample_list will hold exactly 4 items.

sample_list = ['cat', 'dog', 'bunny', 'pig']
print("Your list of animals are: {}, {}, {} and {}".format(*sample_list))

How could I format the string if I do not know the number of items that sample_list will contain at run time? This would mean that I can't enter the appropriate number of bracket place holders at design time.

Answer 1

I'd just use join

sample_list = ['cat', 'dog', 'bunny', 'pig']
printstr = '%s, and %s' % (', '.join(sample_list[:-1]), str(sample_list[-1]))
print("Your list of animals are: %s" % printstr)

Answer 2

If you are on the Python 3.5+ you can use f-strings like:

sample_list = ['cat', 'dog', 'bunny', 'pig']
print(f"Your list of animals are: {', '.join([item for item in sample_list[:-1]])} and {sample_list[-1]}")

f-strings are safer than using % when inputting data and more flexible than .format, for this example it makes no great difference, in my humble opinion one should get used to using them as they are superb :)

Answer 3

This might help.

sample_list = ['cat', 'dog', 'bunny', 'pig']
str_val = ""
l = len(sample_list) -1

for i, v in enumerate(sample_list):
    if i == l:
        str_val += " and {}".format(v)
    else:
        str_val += " {},".format(v)    

print("Your list of animals are: {}".format(str_val))

---

Or one-liner

str_val = "".join(" and {}".format(v) if i == l else " {},".format(v) for i, v in enumerate(sample_list))
print("Your list of animals are: {}".format(str_val))

Output:

Your list of animals are:  cat, dog, bunny, and pig

Answer 4

You could create the string you use format on.

sample_list = ['cat', 'dog', 'bunny', 'pig']
test='Your list of animals are: '+'{}, '*(len(sample_list)-1)+'and {}'
print(test) # Your list of animals are: {}, {}, {}, and {}
print(test.format(*sample_list)) # Your list of animals are: cat, dog, bunny, and pig