Using for loops with nested loops in python

Question

I need to print each element with its atomic number and weight each on a separate line, with a colon between the name and atomic number and weight, however, it prints each three times, I understand why but have no idea how to remedy it. Help

Here is the code I used:

elements = [['beryllium', 4, 9.012], ['magnesium', 12, 24.305], ['calcium', 20, 40.078], ['strontium', 38, 87.620], ['barium', 56, 137.327], ['radium', 88, 266.000]]

for x in elements:
    for i in x:
        print str(x[0]), ':', str(x[1]), str(x[2])

Why do you have the extra for i in x: line? It seems to do nothing except make the code repeat three times. Remove that, that's all. — TheSoundDefense
– TheSoundDefense, Commented Jul 16, 2014 at 16:19
You do not need to call str on each item that you want to print. Doing print x[0], ':', x[1], x[2] would work fine. — user2555451
– user2555451, Commented Jul 16, 2014 at 16:23

Martijn Pieters · Accepted Answer · 2014-07-16 16:33:49Z

4

You are looping over the 3 nested elements; simply remove the nested for:

for x in elements:
    print str(x[0]), ':', str(x[1]), str(x[2])

You can also have Python unpack the elements into separate names; note that the explicit str() calls are not needed here as you are not concatenating the values; let print take care of converting the values to strings for you:

for name, number, weight in elements:
    print name, ':', number, weight

Next, use string formatting to get more control over the output:

for name, number, weight in elements:
    print '{:>10}: {:3d} {:7.3f}'.format(name, number, weight)

and you get nicely formatted output:

>>> for name, number, weight in elements:
...     print '{:>10}: {:3d} {:7.3f}'.format(name, number, weight)
... 
 beryllium:   4   9.012
 magnesium:  12  24.305
   calcium:  20  40.078
 strontium:  38  87.620
    barium:  56 137.327
    radium:  88 266.000

edited Jul 16, 2014 at 16:33

answered Jul 16, 2014 at 16:19

Martijn Pieters

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