In python,what does ++ mean?

Question

I read a script like that

for ... :
   for ...:
      ++i

but what does ++ mean? Is ++ operator is python?

Where did you read that script? I think it may have been a joke or it wasn't actually Python — jamylak, Apr 16 '13 at 12:45
a very strange script .I am a new comer to python,but why python don't offer a convenient operator like count++,any reason? — Ryan_Liu, Apr 16 '13 at 12:48
possible duplicate of [Behaviour of increment and decrement operators in Python](http://stackoverflow.com/questions/1485841/behaviour-of-increment-and-decrement-operators-in-python) — glglgl, Apr 16 '13 at 12:49

score 10 · Answer 1 · answered Apr 16 '13 at 12:44

10

In python, that's just unary plus twice. It doesn't do anything. A single one might coerce a bool to an int, but the second one is totally useless.

answered Apr 16 '13 at 12:44

Pavel Anossov

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This is the best answer :) – jamylak Apr 16 '13 at 12:48
+1 just for the `bool-to-int` point, which hadn't occurred to me at all. – DSM Apr 16 '13 at 14:34

score 6 · Answer 2 · answered Apr 16 '13 at 12:44

6

>>> +1
1
>>> ++1
1
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++1
1

answered Apr 16 '13 at 12:44

jamylak

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6

I think you forgot a `+` in the last line. – Tim Pietzcker Apr 16 '13 at 12:47

score 3 · Answer 3 · answered Apr 16 '13 at 12:44

3

You can use i+=1 instead of i++ for your for loop. There is no ++ usage in Python.

answered Apr 16 '13 at 12:44

Ahmet DAL

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georg · Answer 4 · 2013-04-16T14:31:58.777

Python is an implicitly typed language, therefore, unless we know what type the variable has, we cannot tell for sure what happens if we apply an operator to it. In your example, i is not necessarily an integer, it can be an object with an overloaded unary + (__pos__), for example:

class Duplicator(object):
    def __init__(self, s):
        self.s = s

    def __pos__(self):
        self.s += self.s
        return self

    def __str__(self):
        return self.s

z = Duplicator("ha ")
# 1000 lines of code
print +z
print ++z
print +++z

So the answer to your question "what does ++x mean in python" is "it depends on what x is".

In python,what does ++ mean?

4 Answers4