string methods

[anthonyberet]

I am an abject newbie, so mock away (actually no-one ever does that in
this group..)

Anyway, I want to replace one character in a string, based in that
character's position in the string.

For example if I wanted to replace the 4th character in 'foobar' (the
b)with the contents of another string, newchar, what would be the
easiest way?

I know this touches on immutability etc, but I can't find string methods
to return the first 3 characters, and then the last 2 characters, which
I could concatenate with newchar to make a new string.

I know the string methods are there, but can't find it in any docs, and
just want to check the syntax, unless there is an easier way.

Thanks.

 

[tiissa]

I know this touches on immutability etc, but I can't find string methods
to return the first 3 characters, and then the last 2 characters, which
I could concatenate with newchar to make a new string.

I know the string methods are there, but can't find it in any docs, and
just want to check the syntax, unless there is an easier way.

Strings [1] are sequences [2], and therefore support slicing, which is
what you are looking for.


[1] http://docs.python.org/lib/string-methods.html
[2] http://docs.python.org/lib/typesseq.html

 

[Brian Beck]

I know this touches on immutability etc, but I can't find string methods
to return the first 3 characters, and then the last 2 characters, which
I could concatenate with newchar to make a new string.

As tiissa said, you want slicing:

py> s = "foobar"
py> s[:3]
'foo'
py> s[:3] + "B" + s[4:]
'fooBar'
py>

 

[Peter Hansen]

I know this touches on immutability etc, but I can't find string methods
to return the first 3 characters, and then the last 2 characters, which
I could concatenate with newchar to make a new string.

As tiissa said, you want slicing:

py> s = "foobar"
py> s[:3]
'foo'
py> s[:3] + "B" + s[4:]
'fooBar'

And if that's too ugly for you and you think you need to do this
operation a lot, just define a function to do it for you based on the
index value and string that you pass in to it.

-Peter

 

[Dennis Lee Bieber]

For example if I wanted to replace the 4th character in 'foobar' (the
b)with the contents of another string, newchar, what would be the
easiest way?

s = "foobar"
a = "another"
n = s[:3] + a + s[4:]
n 'fooanotherar'

--

 

[Dennis Lee Bieber]

For example if I wanted to replace the 4th character in 'foobar' (the
b)with the contents of another string, newchar, what would be the
easiest way?

s = "foobar"
a = "another"
n = s[:3] + a + s[4:]
n 'fooanotherar'

--

 

[=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?=]

For example if I wanted to replace the 4th character in 'foobar' (the
b)with the contents of another string, newchar, what would be the
easiest way?

Depends on how your input is specified. If you know it is the b you
want to replace, you write
'foobazar'

There is no issue with immutability here: .replace returns a new
string object, and you assign this to the text variable (thus dropping
the reference to the string "foobar").

If you know it is the fourth character you want to replace, you
do as people have suggested:

>>> text="foobar"
>>> text=text[:3]+"baz"+text[4:]
>>> text

'foobazar'

And, if you know in advance that the string is "foobar", and that
it is the fourth character, and that the replacement string is "baz",
you write



Regards,
Martin