BuggyLemon - 9 months ago 29

Python Question

This code seems to work in Java, but when I convert it to Python, it exceeds the maximum recursion depth and exits.. Not sure what the difference is. They look like they function identically to me.

**Java version:**

`public String addCommas(String number)`

{

if(number.length < 4

{

return number;

}

return addCommas(number.subString(0, number.length - 3)) + "," + number.subString(number.length - 3, number.length);

}

`def addCommas(number):`

number = str(number)

if len(number) < 4:

return number

else:

return addCommas(number[:len(number) - 3] + ',' + number[len(number) - 3:])

Thanks in advance for any help!

Answer

The difference is in the last line.

```
return addCommas(number.subString(0, number.length - 3)) + "," + number.subString(number.length - 3, number.length);
```

This calls `addCommas`

on the first substring only (which reduces the length of the string parameter for the next call by 3) and then appends a comma and the last three digits to its result.

```
return addCommas(number[:len(number) - 3] + ',' + number[len(number) - 3:])
```

This on the other hand first adds a comma and calls `addCommas`

on the whole new string (which is even longer than the original, resulting in the infinite recursion loop).

```
return addCommas(number[:len(number) - 3]) + ',' + number[len(number) - 3:]
```

This would work as it only calls `addCommas`

on the first substring and adds the commas to the result of `addCommas`

, the same way the Java code does it.