DOC: header='infer' is not working when there is no header, closes #17473
- [X] closes #17483

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=h1) Report
> Merging [#18042](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c40c8f8b3baccbd658d078816698f85e3268a781?src=pr&el=desc) will **decrease** coverage by `0.11%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18042/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18042      +/-   ##
==========================================
- Coverage   91.45%   91.33%   -0.12%     
==========================================
  Files         157      164       +7     
  Lines       51378    49802    -1576     
==========================================
- Hits        46987    45487    -1500     
+ Misses       4391     4315      -76
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.13% <ø> (-0.17%)` | :arrow_down: |
| #single | `40.81% <ø> (+0.13%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.59% <ø> (ø)` | :arrow_up: |
| [pandas/core/computation/expressions.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vZXhwcmVzc2lvbnMucHk=) | `0% <0%> (-94.96%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/msgpack/\_version.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL21zZ3BhY2svX3ZlcnNpb24ucHk=) | `44.65% <0%> (-55.35%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.37% <0%> (ø)` | :arrow_up: |
| [pandas/tests/indexes/timedeltas/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL2luZGV4ZXMvdGltZWRlbHRhcy9fX2luaXRfXy5weQ==) | `92.3% <0%> (ø)` | |
| [pandas/tests/util/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL3V0aWwvX19pbml0X18ucHk=) | `100% <0%> (ø)` | |
| [pandas/tests/plotting/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL3Bsb3R0aW5nL19faW5pdF9fLnB5) | `100% <0%> (ø)` | |
| [pandas/tests/io/json/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL2lvL2pzb24vX19pbml0X18ucHk=) | `100% <0%> (ø)` | |
| ... and [6 more](https://codecov.io/gh/pandas-dev/pandas/pull/18042/diff?src=pr&el=tree-more) | |

------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=footer). Last update [c40c8f8...04ee499](https://codecov.io/gh/pandas-dev/pandas/pull/18042?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jorisvandenbossche if you'd review can you rebase Sure thing @jreback  @cmazzullo Seems something went wrong with the rebase (many commits included on github now). In principle if you do exactly the following (assuming pandas-dev/pandas remote is called upstream):

```
git fetch upstream
git checkout gh-17483
git rebase upstream/master
git push origin gh-17483 --force
```

this should solve it. @cmazzullo quickly did the rebase myself. Thanks for this clarification of the docs! Thanks!