Insert some string into given string at given index in Python

Question

I am newbie in Python facing a problem: How to insert some fields in already existing string?

For example, suppose I have read one line from any file which contains:

line = "Name Age Group Class Profession" 

Now I have to insert 3rd Field(Group) 3 times more in the same line before Class field. It means the output line should be:

output_line = "Name Age Group Group Group Group Class Profession" 

I can retrieve 3rd field easily (using split method), but please let me know the easiest way of inserting into the string?

Answer 1

An important point that often bites new Python programmers but the other posters haven't made explicit is that strings in Python are immutable -- you can't ever modify them in place.

You need to retrain yourself when working with strings in Python so that instead of thinking, "How can I modify this string?" instead you're thinking "how can I create a new string that has some pieces from this one I've already gotten?"

Answer 2

For the sake of future 'newbies' tackling this problem, I think a quick answer would be fitting to this thread.

Like bgporter said: Python strings are immutable, and so, in order to modify a string you have to make use of the pieces you already have.

In the following example I insert 'Fu' in to 'Kong Panda', to create 'Kong Fu Panda'

>>> line = 'Kong Panda' >>> index = line.find('Panda') >>> output_line = line[:index] + 'Fu ' + line[index:] >>> output_line 'Kong Fu Panda' 

In the example above, I used the index value to 'slice' the string in to 2 substrings: 1 containing the substring before the insertion index, and the other containing the rest. Then I simply add the desired string between the two and voilà, we have inserted a string inside another.

Python's slice notation has a great answer explaining the subject of string slicing.