## #5769 closed defect (invalid)

# power series are accidentally *mutable* (really dangerous)

Reported by: | was | Owned by: | somebody |
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Priority: | major | Milestone: | sage-duplicate/invalid/wontfix |

Component: | basic arithmetic | Keywords: | |

Cc: | Merged in: | ||

Authors: | Reviewers: | ||

Report Upstream: | N/A | Work issues: | |

Branch: | Commit: | ||

Dependencies: | Stopgaps: |

### Description

wstein@sage:~/build/sage-3.4.1.rc2$ ./sage ---------------------------------------------------------------------- | Sage Version 3.4.1.rc2, Release Date: 2009-04-10 | | Type notebook() for the GUI, and license() for information. | ---------------------------------------------------------------------- Loading Sage library. Current Mercurial branch is: ref2 sage: R.<t> = ZZ[[]] sage: f = 1 + 17*t - 4*t^3 + O(t^5) sage: f[1] = 10 ... IndexError: power series are immutable

Except they are mutable:

sage: f *= 2 sage: f 2 + 34*t - 8*t^3 + O(t^5)

But they shouldn't be! The _imul_ method needs to be deleted.

### Change History (2)

### comment:1 Changed 13 years ago by

Report Upstream: | → N/A |
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Resolution: | → invalid |

Status: | new → closed |

### comment:2 Changed 13 years ago by

Milestone: | sage-4.4.4 → sage-duplicate/invalid/wontfix |
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The code has nothing to do with mutability.

sage: a= (1,2,3)

a is a tuple, an immutable object

sage: a += a sage: a (1, 2, 3, 1, 2, 3)

sage: R.<t> = ZZ[[]] sage: f = 1 + 17*t - 4*t

^{3 + O(t}5) sage: g=f sage: g is f True sage: f+=f sage: f 2 + 34*t - 8*t^{3 + O(t}5) sage: g 1 + 17*t - 4*t^{3 + O(t}5) sage: f is g False