On 04/06/2013 16:21, mstagliamonte wrote:
Hi everyone,
I am a beginner in python and trying to find my way through... :)
I am writing a script to get numbers from the headers of a text file.
If the header is something like:
h01 = ('>scaffold_1')
I just use:
h01.lstrip('>scaffold_')
and this returns me '1'
But, if the header is:
h02: ('>contig-100_0')
if I use:
h02.lstrip('>contig-100_')
this returns me with: ''
...basically nothing. What surprises me is that if I do in this other way:
h02b = h02.lstrip('>contig-100')
I get h02b = ('_1')
and subsequently:
h02b.lstrip('_')
returns me with: '1' which is what I wanted!
Why is this happening? What am I missing?
The methods 'lstrip', 'rstrip' and 'strip' don't strip a string, they
strip characters.
You should think of the argument as a set of characters to be removed.
This code:
h01.lstrip('>scaffold_')
will return the result of stripping the characters '>', '_', 'a', 'c',
'd', 'f', 'l', 'o' and 's' from the left-hand end of h01.
A simpler example:
>>> 'xyyxyabc'.lstrip('xy')
'abc'
It strips the characters 'x' and 'y' from the string, not the string
'xy' as such.
They are that way because they have been in Python for a long time,
long before sets and such like were added to the language.
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