[python] Output first 100 characters in a string

Can seem to find a substring function in python.

Say I want to output the first 100 characters in a string, how can I do this?

I want to do it safely also, meaing if the string is 50 characters it shouldn't fail.

To answer Philipp's concern ( in the comments ), slicing works ok for unicode strings too

>>> greek=u"aß?de??????µ???p??st?f???"
>>> print len(greek)
25
>>> print greek[:10]
aß?de?????

If you want to run the above code as a script, put this line at the top

# -*- coding: utf-8 -*-

If your editor doesn't save in utf-8, substitute the correct encoding

Slicing of arrays is done with [first:last+1].

One trick I tend to use a lot of is to indicate extra information with ellipses. So, if your field is one hundred characters, I would use:

if len(s) <= 100:
    print s
else:
    print "%s..."%(s[:97])

And yes, I know () is superfluous in this case for the % formatting operator, it's just my style.

String formatting using % is a great way to handle this. Here are some examples.

The formatting code '%s' converts '12345' to a string, but it's already a string.

>>> '%s' % '12345'

'12345'

'%.3s' specifies to use only the first three characters.

>>> '%.3s' % '12345'

'123'

'%.7s' says to use the first seven characters, but there are only five. No problem.

>>> '%.7s' % '12345'

'12345'

'%7s' uses up to seven characters, filling missing characters with spaces on the left.

>>> '%7s' % '12345'

'  12345'

'%-7s' is the same thing, except filling missing characters on the right.

>>> '%-7s' % '12345'

'12345  '

'%5.3' says use the first three characters, but fill it with spaces on the left to total five characters.

>>> '%5.3s' % '12345'

'  123'

Same thing except filling on the right.

>>> '%-5.3s' % '12345'

'123  '

Can handle multiple arguments too!

>>> 'do u no %-4.3sda%3.2s wae' % ('12345', 6789)

'do u no 123 da 67 wae'

If you require even more flexibility, str.format() is available too. Here is documentation for both.

Most of previous examples will raise an exception in case your string is not long enough.

Another approach is to use 'yourstring'.ljust(100)[:100].strip().

This will give you first 100 chars. You might get a shorter string in case your string last chars are spaces.

From python tutorial:

Degenerate slice indices are handled gracefully: an index that is too large is replaced by the string size, an upper bound smaller than the lower bound returns an empty string.

So it is safe to use x[:100].

Easy:

print mystring[:100]

[start:stop:step]

So If you want to take only 100 first character, use your_string[0:100] or your_string[:100] If you want to take only the character at even position, use your_string[::2] The "default values" for start is 0, for stop - len of string, and for step - 1. So when you don't provide one of its and put ':', it'll use it default value.