Construct 1d array from listlike
State: closed

- [x] tests passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

#18626 isn't converging, will need more work and I won't have much time soon, so I took away the asv and refactoring that should be straighforward to merge.

asv says

```
       before           after         ratio
     [96439fb1]       [e72437c5]
-        38.6±1ms       35.1±0.5ms     0.91  panel_ctor.Constructors3.time_panel_from_dict_same_index
-      24.2±0.1μs       21.8±0.2μs     0.90  ctors.Constructors.time_index_from_array_string
-        39.7±1ms      34.9±0.02ms     0.88  panel_ctor.Constructors2.time_panel_from_dict_equiv_indexes
-     14.1±0.04μs      12.3±0.08μs     0.87  ctors.Constructors.time_series_from_ndarray
-      12.2±0.6μs      10.1±0.05μs     0.82  ctors.Constructors.time_dtindex_from_series

SOME BENCHMARKS HAVE CHANGED SIGNIFICANTLY.
```

... but they are borderline, and don't always come up.



Labels:
name: Reshaping
description: Concat, Merge/Join, Stack/Unstack, Explode
name: Dtype Conversions
description: Unexpected or buggy dtype conversions

Comments:
@jreback  Any hint about why all 2.7 fail with "``ImportError: C extension: lib not built. If you want to import pandas from the source directory, you may need to run 'python setup.py build_ext --inplace --force' to build the C extensions first.``"?
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=h1) Report
> Merging [#18769](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7a0ee19e95e29042c3373a1d912d2db27108c828?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18769/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18769      +/-   ##
==========================================
- Coverage   91.64%   91.59%   -0.05%     
==========================================
  Files         154      154              
  Lines       51401    51430      +29     
==========================================
+ Hits        47106    47108       +2     
- Misses       4295     4322      +27
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.46% <100%> (-0.03%)` | :arrow_down: |
| #single | `40.83% <80%> (-0.13%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.6% <100%> (+0.07%)` | :arrow_up: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `91.77% <100%> (ø)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `92.92% <100%> (-0.09%)` | :arrow_down: |
| [pandas/core/algorithms.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWxnb3JpdGhtcy5weQ==) | `94.14% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `64.78% <0%> (-1.74%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `82.71% <0%> (-0.44%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.68% <0%> (-0.11%)` | :arrow_down: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.55% <0%> (+0.05%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=footer). Last update [7a0ee19...e5b3cd5](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

> Any hint about why all 2.7 fail with

Answering myself... it was a circular dependency
Hello @toobaz! Thanks for updating the PR.



















Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on December 19, 2017 at 13:39 Hours UTC
> We are not using the dtype argument. So just eliminate it. I don't see utility in having it.

Yeah, but this is hardly an argument - you're not even seeing that the change you are firmly pretending in the code is in contrast with the change you are firmly pretending in the test.

But I guess I'll have to explain you in some other PR, now I don't have enough time.

An updated version of this one is on its way.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@b32dd63`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18769/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #18769   +/-   ##
=========================================
  Coverage          ?   91.62%           
=========================================
  Files             ?      154           
  Lines             ?    51401           
  Branches          ?        0           
=========================================
  Hits              ?    47097           
  Misses            ?     4304           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.49% <100%> (?)` | |
| #single | `40.84% <80%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `92.92% <100%> (ø)` | |
| [pandas/core/algorithms.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWxnb3JpdGhtcy5weQ==) | `94.14% <100%> (ø)` | |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.6% <100%> (ø)` | |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/18769/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `91.77% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=footer). Last update [b32dd63...d0a6e48](https://codecov.io/gh/pandas-dev/pandas/pull/18769?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

this will fail because of a conda issue, that I think is now fixed in master. I will merge after this is resolved (no need to repush).
thanks!