Archive
Reverse an integer
Exercise
Take an integer and reverse its digits. The result is also an integer. Example: 83657 becomes 75638.
Solution
#!/usr/bin/env python
def reverse_int(n):
return int(str(n)[::-1])
n = 83657
print n # 83657
print reverse_int(n) # 75638
Summary: convert the number to string, reverse the string, then convert it back to integer. Details: 83657 -> str(83657) returns "83657" which is a string -> reverse it, we get "75638" -> int("75638") converts it to an integer.
Notes
If you want to concatenate a string and an integer, first you need to convert the integer to string. Example:
n = 83657 print "The value of n is " + n # error, won't work print "The value of n is " + str(n) # OK
Pretty print an integer
Exercise: Take an integer and print it in a pretty way, i.e. use commas as thousands separators. Example: 1977 should be 1,977.
Solution:
#!/usr/bin/env python
def numberToPrettyString(n):
"""Converts a number to a nicely formatted string.
Example: 6874 => '6,874'."""
l = []
for i, c in enumerate(str(n)[::-1]):
if i%3==0 and i!=0:
l += ','
l += c
return "".join(l[::-1])
#
if __name__ == "__main__":
number = 6874
print numberToPrettyString(number) # '6,874'
The idea is simple. Consider the number 1977. Convert it to string ("1977") and reverse it ("7791"). Start processing it from left to right and after every third character add a comma: "7" -> "77" -> "779," (comma added) -> "779,1". Now reverse the string ("1,977"). Done.
Links
- http://stackoverflow.com/questions/1823058/how-to-print-number-with-commas-as-thousands-separators-in-python-2-x (for some more possible solutions)
Update (20131125)
There is an easier way. You can do it with string formatting too:
>>> n = 1977
>>> "{:,}".format(n)
'1,977'
Thanks to Krisztián B. for the tip.
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