Code Sample, a copy-pastable example if possible

pd.Timedelta(1,unit='M')
Out[119]: Timedelta('30 days 10:29:06')

pd.Timedelta(2,unit='M')
Out[120]: Timedelta('60 days 20:58:12')

pd.Timedelta(1,unit='d')
Out[121]: Timedelta('1 days 00:00:00')

Problem description

only month has problem. day and week works #fine. pandas version 0.19 yield right result ,but 0.20+ goes wrong

Expected Output

Output of pd.show_versions()

pd.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.6.1.final.0 python-bits: 64 OS: Windows OS-release: 10 machine: AMD64 processor: Intel64 Family 6 Model 60 Stepping 3, GenuineIntel byteorder: little LC_ALL: None LANG: en LOCALE: None.None pandas: 0.20.1 pytest: 3.0.7 pip: 9.0.1 setuptools: 35.0.1 Cython: 0.25.2 numpy: 1.12.1 scipy: 0.19.0 xarray: None IPython: 6.0.0 sphinx: 1.5.5 patsy: 0.4.1 dateutil: 2.6.0 pytz: 2017.2 blosc: None bottleneck: 1.2.0 tables: 3.2.2 numexpr: 2.6.2 feather: None matplotlib: 2.0.1 openpyxl: 2.4.1 xlrd: 1.0.0 xlwt: 1.2.0 xlsxwriter: 0.9.6 lxml: 3.7.3 bs4: 4.5.3 html5lib: 0.999999999 sqlalchemy: 1.1.9 pymysql: 0.7.11.None psycopg2: None jinja2: 2.9.6 s3fs: None pandas_gbq: None pandas_datareader: None

Comment From: jorisvandenbossche

Can you show the output that you think is correct for pandas 0.19 ?

I get a consistent (but maybe wrong, that could be discussed) output for the latest releases:

In [52]: pd.__version__
Out[52]: '0.21.0.dev+19.g69a5d6f.dirty'

In [53]: pd.Timedelta(1, unit='M')
Out[53]: Timedelta('30 days 10:29:06')

In [2]: pd.__version__
Out[2]: '0.19.2'

In [3]: pd.Timedelta(1, unit='M')
Out[3]: Timedelta('30 days 10:29:06')

In [1]: pd.__version__
Out[1]: u'0.18.1'

In [2]: pd.Timedelta(1, unit='M')
Out[2]: Timedelta('30 days 10:29:06')

That said, I think we should actually disallow the M unit, as this does not make sense. Timedelta is made for fixed intervals (with a fixed length), not for relative / variable length periods (which a 'month' is, in constrast with eg a 'day')

Comment From: jreback

xref to #12691

this was for numpy compat. I agree, let's deprecate passing 'M', 'Y' on construction (see also the xref #12691 where they are passed as strings).

Comment From: jorisvandenbossche

@jreback opened an new issue for the deprecation (the top post is then cleaner)

@princelai Closing this issue, as I don't see a difference between 0.19.2 and 0.20.1. But if you actually see it, please post the full output of code and result in both versions.