pandas resample weekly and interpolate - wrong results
```python
import pandas as pd
```


```python
pd.show_versions()
```

    
    INSTALLED VERSIONS
    ------------------
    commit: None
    python: 3.5.3.final.0
    python-bits: 64
    OS: Windows
    OS-release: 10
    machine: AMD64
    processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
    byteorder: little
    LC_ALL: None
    LANG: None
    LOCALE: None.None
    
    pandas: 0.20.1
    pytest: 2.9.2
    pip: 8.1.2
    setuptools: 34.4.1
    Cython: 0.24.1
    numpy: 1.12.1
    scipy: 0.19.0
    xarray: None
    IPython: 5.3.0
    sphinx: 1.4.6
    patsy: 0.4.1
    dateutil: 2.6.0
    pytz: 2016.6.1
    blosc: None
    bottleneck: 1.2.0
    tables: 3.2.2
    numexpr: 2.6.2
    feather: None
    matplotlib: 2.0.0
    openpyxl: 2.3.2
    xlrd: 1.0.0
    xlwt: 1.1.2
    xlsxwriter: 0.9.3
    lxml: 3.7.2
    bs4: 4.5.3
    html5lib: 0.999999999
    sqlalchemy: 1.0.13
    pymysql: None
    psycopg2: None
    jinja2: 2.9.6
    s3fs: None
    pandas_gbq: None
    pandas_datareader: None
    


```python
pd.date_range("1900/01/01","1900/12/31",freq='M')
```




    DatetimeIndex(['1900-01-31', '1900-02-28', '1900-03-31', '1900-04-30',
                   '1900-05-31', '1900-06-30', '1900-07-31', '1900-08-31',
                   '1900-09-30', '1900-10-31', '1900-11-30', '1900-12-31'],
                  dtype='datetime64[ns]', freq='M')




```python
pdtest=pd.DataFrame(data=list(range(12,0,-1)),index=pd.date_range("1900/01/01","1900/12/31",freq='M'))
pdtest
```




<div>
<table border="1" class="dataframe">
  <thead>
    <tr style="text-align: right;">
      <th></th>
      <th>0</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th>1900-01-31</th>
      <td>12</td>
    </tr>
    <tr>
      <th>1900-02-28</th>
      <td>11</td>
    </tr>
    <tr>
      <th>1900-03-31</th>
      <td>10</td>
    </tr>
    <tr>
      <th>1900-04-30</th>
      <td>9</td>
    </tr>
    <tr>
      <th>1900-05-31</th>
      <td>8</td>
    </tr>
    <tr>
      <th>1900-06-30</th>
      <td>7</td>
    </tr>
    <tr>
      <th>1900-07-31</th>
      <td>6</td>
    </tr>
    <tr>
      <th>1900-08-31</th>
      <td>5</td>
    </tr>
    <tr>
      <th>1900-09-30</th>
      <td>4</td>
    </tr>
    <tr>
      <th>1900-10-31</th>
      <td>3</td>
    </tr>
    <tr>
      <th>1900-11-30</th>
      <td>2</td>
    </tr>
    <tr>
      <th>1900-12-31</th>
      <td>1</td>
    </tr>
  </tbody>
</table>
</div>




```python
pdtest.resample('D').interpolate()[:15]
```




<div>
<table border="1" class="dataframe">
  <thead>
    <tr style="text-align: right;">
      <th></th>
      <th>0</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th>1900-01-31</th>
      <td>12.000000</td>
    </tr>
    <tr>
      <th>1900-02-01</th>
      <td>11.964286</td>
    </tr>
    <tr>
      <th>1900-02-02</th>
      <td>11.928571</td>
    </tr>
    <tr>
      <th>1900-02-03</th>
      <td>11.892857</td>
    </tr>
    <tr>
      <th>1900-02-04</th>
      <td>11.857143</td>
    </tr>
    <tr>
      <th>1900-02-05</th>
      <td>11.821429</td>
    </tr>
    <tr>
      <th>1900-02-06</th>
      <td>11.785714</td>
    </tr>
    <tr>
      <th>1900-02-07</th>
      <td>11.750000</td>
    </tr>
    <tr>
      <th>1900-02-08</th>
      <td>11.714286</td>
    </tr>
    <tr>
      <th>1900-02-09</th>
      <td>11.678571</td>
    </tr>
    <tr>
      <th>1900-02-10</th>
      <td>11.642857</td>
    </tr>
    <tr>
      <th>1900-02-11</th>
      <td>11.607143</td>
    </tr>
    <tr>
      <th>1900-02-12</th>
      <td>11.571429</td>
    </tr>
    <tr>
      <th>1900-02-13</th>
      <td>11.535714</td>
    </tr>
    <tr>
      <th>1900-02-14</th>
      <td>11.500000</td>
    </tr>
  </tbody>
</table>
</div>




```python
pdtest.resample('W-MON').interpolate()
```




<div>
<table border="1" class="dataframe">
  <thead>
    <tr style="text-align: right;">
      <th></th>
      <th>0</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th>1900-02-05</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-02-12</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-02-19</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-02-26</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-03-05</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-03-12</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-03-19</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-03-26</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-04-02</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-04-09</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-04-16</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-04-23</th>
      <td>NaN</td>
    </tr>
    <tr>
      <th>1900-04-30</th>
      <td>9.000000</td>
    </tr>
    <tr>
      <th>1900-05-07</th>
      <td>8.771429</td>
    </tr>
    <tr>
      <th>1900-05-14</th>
      <td>8.542857</td>
    </tr>
    <tr>
      <th>1900-05-21</th>
      <td>8.314286</td>
    </tr>
    <tr>
      <th>1900-05-28</th>
      <td>8.085714</td>
    </tr>
    <tr>
      <th>1900-06-04</th>
      <td>7.857143</td>
    </tr>
    <tr>
      <th>1900-06-11</th>
      <td>7.628571</td>
    </tr>
    <tr>
      <th>1900-06-18</th>
      <td>7.400000</td>
    </tr>
    <tr>
      <th>1900-06-25</th>
      <td>7.171429</td>
    </tr>
    <tr>
      <th>1900-07-02</th>
      <td>6.942857</td>
    </tr>
    <tr>
      <th>1900-07-09</th>
      <td>6.714286</td>
    </tr>
    <tr>
      <th>1900-07-16</th>
      <td>6.485714</td>
    </tr>
    <tr>
      <th>1900-07-23</th>
      <td>6.257143</td>
    </tr>
    <tr>
      <th>1900-07-30</th>
      <td>6.028571</td>
    </tr>
    <tr>
      <th>1900-08-06</th>
      <td>5.800000</td>
    </tr>
    <tr>
      <th>1900-08-13</th>
      <td>5.571429</td>
    </tr>
    <tr>
      <th>1900-08-20</th>
      <td>5.342857</td>
    </tr>
    <tr>
      <th>1900-08-27</th>
      <td>5.114286</td>
    </tr>
    <tr>
      <th>1900-09-03</th>
      <td>4.885714</td>
    </tr>
    <tr>
      <th>1900-09-10</th>
      <td>4.657143</td>
    </tr>
    <tr>
      <th>1900-09-17</th>
      <td>4.428571</td>
    </tr>
    <tr>
      <th>1900-09-24</th>
      <td>4.200000</td>
    </tr>
    <tr>
      <th>1900-10-01</th>
      <td>3.971429</td>
    </tr>
    <tr>
      <th>1900-10-08</th>
      <td>3.742857</td>
    </tr>
    <tr>
      <th>1900-10-15</th>
      <td>3.514286</td>
    </tr>
    <tr>
      <th>1900-10-22</th>
      <td>3.285714</td>
    </tr>
    <tr>
      <th>1900-10-29</th>
      <td>3.057143</td>
    </tr>
    <tr>
      <th>1900-11-05</th>
      <td>2.828571</td>
    </tr>
    <tr>
      <th>1900-11-12</th>
      <td>2.600000</td>
    </tr>
    <tr>
      <th>1900-11-19</th>
      <td>2.371429</td>
    </tr>
    <tr>
      <th>1900-11-26</th>
      <td>2.142857</td>
    </tr>
    <tr>
      <th>1900-12-03</th>
      <td>1.914286</td>
    </tr>
    <tr>
      <th>1900-12-10</th>
      <td>1.685714</td>
    </tr>
    <tr>
      <th>1900-12-17</th>
      <td>1.457143</td>
    </tr>
    <tr>
      <th>1900-12-24</th>
      <td>1.228571</td>
    </tr>
    <tr>
      <th>1900-12-31</th>
      <td>1.000000</td>
    </tr>
  </tbody>
</table>
</div>




