How to remove the trailing comma from a loop in Python?

Question

Here is my code so far:

def main():
    for var in range (1, 101):
        num= IsPrime(var)
        if num == 'true':
             print(var, end=', ')

The IsPrime function calculates whether or not a function is prime.

I need to print out the prime numbers from 1 to 100 formatted into a single line with commas and spaces in between. for example, output should look like:

2,  3,  5,  7,  11,  13,  17,  19,  23,  29,  31,  37,  41,  43,  47,  53,  59,  61,  67,  71,  73,  79,  83,  89,  97

I tried to run my program, but I always get a trailing comma at the end of 97. I don't know how to remove the comma, and because it is a loop, str.rstrip and [:-1] don't work.

I need to use a loop and I can't use

print('2') 
print(', ', var, end='')

for the other prime numbers.

I can't tell if there's an easier way to code this or I'm not aware of a function that can do this correctly.

IsPrime(var) should be returning a boolean not a string then if IsPrime(var) would be sufficient to check — Padraic Cunningham
– Padraic Cunningham, Commented Jul 19, 2015 at 23:52

wjandrea · Accepted Answer · 2021-07-09 01:14:58Z

10

The idiomatic Python code in my opinion would look something like this:

print(', '.join([str(x) for x in xrange(1, 101) if IsPrime(x) == 'true']))

(Things would be better if IsPrime actually returned True or False instead of a string)

This is functional instead of imperative code.

If you want imperative code, you should print the ', ' before each element excepting the first item of the loop. You can do this with a boolean variable which you set to true after you've seen one item.

edited Jul 9, 2021 at 1:14

wjandrea

33.8k10 gold badges69 silver badges105 bronze badges

answered Jul 19, 2015 at 20:13

Borealid

99.3k9 gold badges111 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

koffein Over a year ago

Would be even more pythonic, if you deleted the [ ... ] around the expression. Then it would just be a light-weight generator that is passed to the join-method...

Borealid Over a year ago

@koffein Not bad at all! I like filter myself, as it works in pretty much any functional programming language.

koffein Over a year ago

Well, in this case ifilter from itertools would be a function to consider, because as far as I know filter returns a list, just like the list comprehension with [ ... ] up there. I personally do not like filter, if I have to create a lambda inline. I a function already exists, its fine, but otherwise it looks more crowded to me then the list-comprehension/generator...

Padraic Cunningham Over a year ago

@koffein, that would actually be worse as python then still has to build a list for join.

mstuebner Over a year ago

Am I wrong when I say that print(', '.join([x for x in xrange(1, 101) if IsPrime(x) == 'true'])) fails at all, as join() expects a string but gets an int? So it misses an str(x), doesn't it?

|

Daniele Pantaleone · Accepted Answer · 2015-07-19 20:13:15Z

5

You can put all the numbers into a list and then join all the values:

def main():
    primes = []
    for var in range (1, 101):
        if IsPrime(var) == 'true':
            primes.append(var)
        num = IsPrime(var)
    print(', '.join(primes))

answered Jul 19, 2015 at 20:13

Daniele Pantaleone

2,75324 silver badges34 bronze badges

Collectives™ on Stack Overflow

How to remove the trailing comma from a loop in Python?

2 Answers 2

8 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

8 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related