create DataFrame from dict with different data type, cat't change value then.
## I try to make a DataFrame from a dict, and need to change it's value then. I find when dict as different data type value, It does't work.
# dict has same data type, It works.

from pandas import DataFrame  
a = {'a': 1, 'b': 1}
df = DataFrame([a])
print df
rec = df.ix[0]
rec['a'] = 100
print df

out:
   a  b
0  1  1
     a  b
0  100  1
# dict has different data type, go wrong.

from pandas import DataFrame
a = {'a': 1, 'b': '1'}
df = DataFrame([a])
print df
rec = df.ix[0]
rec['a'] = 100
print df

out:
   a  b
0  1  1
   a  b
0  1  1

-c:6: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

See the the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
