CLN16668: remove OrderedDefaultDict
 - [x] closes #16668
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [ ] whatsnew entry

The replacement of usage covered by tests.
Hello @faic! Thanks for updating the PR.

 - In the file [`pandas/compat/__init__.py`](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py), following are the PEP8 issues :

> [Line 61:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L61): [E402](https://duckduckgo.com/?q=pep8%20E402) module level import not at top of file
> [Line 174:5](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L174): [E731](https://duckduckgo.com/?q=pep8%20E731) do not assign a lambda expression, use a def
> [Line 221:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L221): [E305](https://duckduckgo.com/?q=pep8%20E305) expected 2 blank lines after class or function definition, found 1
> [Line 245:80](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L245): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (90 > 79 characters)
> [Line 278:9](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L278): [E722](https://duckduckgo.com/?q=pep8%20E722) do not use bare except'
> [Line 297:80](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L297): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (90 > 79 characters)
> [Line 337:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L337): [E305](https://duckduckgo.com/?q=pep8%20E305) expected 2 blank lines after class or function definition, found 1
> [Line 337:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L337): [E402](https://duckduckgo.com/?q=pep8%20E402) module level import not at top of file
> [Line 360:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L360): [E402](https://duckduckgo.com/?q=pep8%20E402) module level import not at top of file
> [Line 361:1](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/compat/__init__.py#L361): [E402](https://duckduckgo.com/?q=pep8%20E402) module level import not at top of file

 - In the file [`pandas/core/panel.py`](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/core/panel.py), following are the PEP8 issues :

> [Line 1011:13](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/core/panel.py#L1011): [E731](https://duckduckgo.com/?q=pep8%20E731) do not assign a lambda expression, use a def
> [Line 1125:9](https://github.com/pandas-dev/pandas/blob/1dc417e00ad6338ce181b9636c8e6911363d7f1b/pandas/core/panel.py#L1125): [E731](https://duckduckgo.com/?q=pep8%20E731) do not assign a lambda expression, use a def



##### Comment last updated on July 15, 2017 at 13:18 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=h1) Report
> Merging [#16939](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ad24759871ea43131711cfce1e5fc69c06d82956?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16939/graphs/tree.svg?src=pr&width=650&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16939      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         161      161              
  Lines       49306    49289      -17     
==========================================
- Hits        44868    44846      -22     
- Misses       4438     4443       +5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (ø)` | :arrow_up: |
| #single | `40.19% <25%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `60.67% <ø> (-1.55%)` | :arrow_down: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `96.94% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.71% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16939?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/16939?src=pr&el=footer). Last update [ad24759...2f64621](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=h1) Report
> Merging [#16939](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ad24759871ea43131711cfce1e5fc69c06d82956?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16939/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16939      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         161      161              
  Lines       49306    49289      -17     
==========================================
- Hits        44868    44846      -22     
- Misses       4438     4443       +5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (ø)` | :arrow_up: |
| #single | `40.19% <25%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `60.67% <ø> (-1.55%)` | :arrow_down: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `96.94% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.71% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16939?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/16939?src=pr&el=footer). Last update [ad24759...1dc417e](https://codecov.io/gh/pandas-dev/pandas/pull/16939?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. ping on green. thanks!