Iterating through python list and outputting numbers to a list

Question

I've been racking my brain for a few days now. I'm fairly new to Python and trying to figure out how to split a string and output the desired contents to a list. I'm trying to select an entire number (regardless of the number of digits in the number) from a string and store it in a variable for future use. My list of strings will look something like this:

["<foo>1</foo>", "<foo>2</foo>", "<foo>3</foo>", "<foo>4</foo>", "<foo>5</foo>", "<foo>6</foo>", "<foo>7</foo>", "<foo>8</foo>", "<foo>9</foo>", "<foo>10</foo>"]

I'm fairly familiar with for loops and the basic concepts of python, but not sure if I've bitten off more than I can chew.

EDIT: I do already have the list in my script. The challenge is to drop the characters surrounding the numbers, leaving only the numbers in the list.

Bill M. · Accepted Answer · 2018-11-28 21:24:17Z

1

Python's list() function will turn any string into a list. Also, when you do a for loop on a string, it will iterate every character. So since what you want is a list whose items are <foo> </foo> surrounding every digit in your string:

>>> n = 1234567
>>> L = [ ('<foo>%s</foo>' % i) for i in list(str(n)) ]
>>> print(L)
['<foo>1</foo>', '<foo>2</foo>', '<foo>3</foo>', '<foo>4</foo>', '<foo>5</foo>', '<foo>6</foo>', '<foo>7</foo>']

answered Nov 28, 2018 at 21:24

Bill M.

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user8408080 · Accepted Answer · 2018-11-28 21:40:25Z

0

I suppose, that you have this as your input (if I understood you correctly):

a = ["<foo>1</foo>", "<foo>2</foo>", "<foo>3</foo>", "<foo>4</foo>", "<foo>5</foo>", "<foo>6</foo>", "<foo>7</foo>", "<foo>8</foo>", "<foo>9</foo>", "<foo>10</foo>"]

The easiest way to find things in a string is a regular expression. Python has the re module for this. As you know list comprehension already, here is a short way of finding all the numbers:

b = [int(re.search(r"\d+", element).group()) for element in a]

\d+ searches for one or more (+) digit (\d).

answered Nov 28, 2018 at 21:40

user8408080

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1 Comment

Bill DeCastro Over a year ago

Much appreciated!

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