how to find the syntax error

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Hi

Here's a short code (copy-paste) that gets me syntax error i=3 while i>0 : print i, 'looping'    i=i-1

"<ipython-input-7-8e7eba3f21a0>", line 4 i=i-Integer(1)

I retyped it a second time; now it works, but I don't see any difference. i=3 while i>0 : print i, 'looping' i=i-1

Retyping only the line 4 with the error won't help, retyping the previous lines or restarting the kernel won't help either. It's like a phantom error