Pandas change column value if greater than len

I am trying to use an if statement to change values within a column if there length is greater than x

My csv data ..

  ID            Test_Case                                            TC_NUM
14581,dialog_testcase_4000.0134_mvp_not_understood-inprogress.xml,4000.0134
14582,dialog_testcase_4000.0135_mvp_not_understood-inprogress.xml,4000.0135
14583,dialog_testcase_4000.0136_mvp_not_understood-inprogress.xml,4000.0136
14584,dialog_testcase_4000.0137_mvp_not_understood_6.2.0-inprogress.xml,4000.01376.2.0
14585,dialog_testcase_4000.0138_mvp_not_understood_6.2.0-inprogress.xml,4000.01386.2.0

What I want:

  ID            Test_Case                                            TC_NUM
14581,dialog_testcase_4000.0134_mvp_not_understood-inprogress.xml,4000.0134
14582,dialog_testcase_4000.0135_mvp_not_understood-inprogress.xml,4000.0135
14583,dialog_testcase_4000.0136_mvp_not_understood-inprogress.xml,4000.0136
14584,dialog_testcase_4000.0137_mvp_not_understood_6.2.0-inprogress.xml,4000.0137
14585,dialog_testcase_4000.0138_mvp_not_understood_6.2.0-inprogress.xml,4000.0138

My current code is able to extract some of the right columns, but messes up if additional numbers are in there.

df1['TC_NUM'] = df1['TC_NUM'].str.replace(r'[^0-9.]+', '')

df1['TC_NUM'] = df1['TC_NUM'].str[:-1]

My thought/attempt as using an if statement to correct this.

if dfidtcnum(len['TC_NUM'] > 12):
    print "True"