Making a string out of a string and an integer in Python

Question

I get this error when trying to take an integer and prepend "b" to it, converting it into a string:

  File "program.py", line 19, in getname
    name = "b" + num
TypeError: Can't convert 'int' object to str implicitly

That's related to this function:

num = random.randint(1,25)
name = "b" + num

[This SO answer](https://stackoverflow.com/a/6380529/2071807) addresses why Python doesn't just cast the RHS of `+` to a `str` like Javascript does. It was kind of surprising to me but that answer explains it well. — LondonRob, Oct 11 '17 at 10:07

score 45 · Accepted Answer · edited Jul 27 '22 at 02:11

45

name = 'b' + str(num)

or

name = 'b%s' % num

Note that the second approach is deprecated in 3.x.

edited Jul 27 '22 at 02:11

Karl Knechtel

answered May 12 '10 at 22:30

msw

The % is deprecated in Python 3. Might want to remove that one. – S.Lott May 12 '10 at 22:32
3

@S.Lott I have to work on some systems using python <2.6, namely Ubuntu 8.04. I didn't realize .format wasn't available, and after developing the code on Python 2.6, having to go and change all the .format commands to % was a bit of a pain. So, actually, while I prefer .format, if you need compatibility with every version, % is still your best bet - it IS present in Python 3, while .format is not present in python 2.5 and below. – JAL May 12 '10 at 22:36
4

@S.Lott % is not deprecated in Python3. [PEP 3101](https://www.python.org/dev/peps/pep-3101/) clearly mentions that *The new system does not collide with any of the method names of the existing string formatting techniques, so both systems can co-exist until it comes time to deprecate the older system.* – Bhargav Rao Nov 05 '16 at 18:40

score 11 · Answer 2 · edited Nov 30 '20 at 20:13

11

Python won't automatically convert types in the way that languages such as JavaScript or PHP do.

You have to convert it to a string, or use a formatting method.

name="b"+str(num)

or printf style formatting (this has been deprecated in python3)

name="b%s" % (num,)

or the new .format string method

name="b{0}".format(num)

edited Nov 30 '20 at 20:13

lugiorgi

answered May 12 '10 at 22:30

JAL

The % is deprecated in Python 3. Might want to remove that one. – S.Lott May 12 '10 at 22:31
2

I can't edit it now it seems, so noted here that % is deprecated. Also worth mentioning is that .format isn't available before Python 2.6. – JAL May 13 '10 at 00:34

score 3 · Answer 3 · edited Apr 28 '18 at 13:01

3

Python 3.6 has f-strings where you can directly put the variable names without the need to use format:

>>> num=12
>>> f"b{num}"
'b12'

edited Apr 28 '18 at 13:01

Georgy

answered Apr 28 '18 at 12:58

score 2 · Answer 4 · answered May 12 '10 at 22:30

2

Yeah, python doesn't having implicit int to string conversions.

try str(num) instead

answered May 12 '10 at 22:30

Alan

score 0 · Answer 5 · answered May 12 '10 at 22:31

0

name = "b{0:d}".format( num )

answered May 12 '10 at 22:31

S.Lott

5 Answers5