python 2 vs python 3 columns ordering using pandas
#### Code Sample

```python
selective_price = []
for index_sample, row_sample in selectivePriceList.iterrows():
    selective_price.append(row_sample.loc[list_keys])
    counter +=1
    #print(selective_price)  
selective_price = pd.concat(selective_price, axis=1) 
selective_price = selective_price.transpose()
selective_price.insert(0, "Date", DateFrame.loc[index:index+(w-1)], allow_duplicates=False)
#print(selective_price)
start_end_date = str(DateFrame[index]) + "_" + str(DateFrame[index+(w-1)])
#print (start_end_date)
selective_price = selective_price.sort_values(by=['Date'])
print (selective_price.columns)
selective_price.to_csv('rolling_results_'+start_end_date+"_.csv",index=False)

```
#### Problem description

I am facing an issue related to column ordering in pandas data frame while saving it as csv. This is the ordering in python 3:
![image](https://user-images.githubusercontent.com/25582838/36163895-6c489c70-10f3-11e8-896a-4311757741c7.png)


while in python 2 , it reverts the columns and also if the number of column is larger than 2 the ordering is totally different 
![image](https://user-images.githubusercontent.com/25582838/36164402-ea4928be-10f4-11e8-8a8d-fac4b344efca.png)


#### Expected Output

#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
for python 3

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.3.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 69 Stepping 1, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.21.0
pytest: None
pip: 9.0.1
setuptools: 28.8.0
Cython: None
numpy: 1.13.3
scipy: 1.0.0
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.1.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None




for python 2


INSTALLED VERSIONS
------------------
commit: None
python: 2.7.14.final.0
python-bits: 32
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 69 Stepping 1, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.22.0
pytest: None
pip: 9.0.1
setuptools: 28.8.0
Cython: None
numpy: 1.14.0
scipy: None
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.1.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
