Python: Is there an equivalent of mid, right, and left from BASIC?

Question

I want to do something like this:

    >>> mystring = "foo"
    >>> print(mid(mystring))

Help!

Solution 1

slices to the rescue :)

def left(s, amount):
    return s[:amount]

def right(s, amount):
    return s[-amount:]

def mid(s, offset, amount):
    return s[offset:offset+amount]

Solution 2

If I remember my QBasic, right, left and mid do something like this:

>>> s = '123456789'
>>> s[-2:]
'89'
>>> s[:2]
'12'
>>> s[4:6]
'56'

http://www.angelfire.com/scifi/nightcode/prglang/qbasic/function/strings/left_right.html

Solution 3

Thanks Andy W

I found that the mid() did not quite work as I expected and I modified as follows:

def mid(s, offset, amount):
    return s[offset-1:offset+amount-1]

I performed the following test:

print('[1]23', mid('123', 1, 1))
print('1[2]3', mid('123', 2, 1))
print('12[3]', mid('123', 3, 1))
print('[12]3', mid('123', 1, 2))
print('1[23]', mid('123', 2, 2))

Which resulted in:

[1]23 1
1[2]3 2
12[3] 3
[12]3 12
1[23] 23

Which was what I was expecting. The original mid() code produces this:

[1]23 2
1[2]3 3
12[3] 
[12]3 23
1[23] 3

But the left() and right() functions work fine. Thank you.

Solution 4

This is Andy's solution. I just addressed User2357112's concern and gave it meaningful variable names. I'm a Python rookie and preferred these functions.

def left(aString, howMany):
    if howMany <1:
        return ''
    else:
        return aString[:howMany]

def right(aString, howMany):
    if howMany <1:
        return ''
    else:
        return aString[-howMany:]

def mid(aString, startChar, howMany):
    if howMany < 1:
        return ''
    else:
        return aString[startChar:startChar+howMany]

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Comments

[user2357112]

Careful with that right function. 'asdf'[-0:] == 'asdf', not ''.

[Andy W]

@user2357112 sure, you are correct. The code was provided rather for illustartive purpose to show how the functions in Python and Basic might correspond

[Bowdzone]

This is really a comment, not an answer. With a bit more rep, you will be able to post comments. Please use answers only for posting actual answers.

[user96931]

Don't forget: left() and right() may return an error if amount is > than the amount of characters in s.

[user96931]

The mid() function has to be replaced by the answer below.

[Caltor]

right and left in basic return a portion of the string, not a boolean.