#### Code Sample, a copy-pastable example if possible From this stackoverflow [question](https://stackoverflow.com/q/45453508/2336654) ```python import pandas as pd df = pd.DataFrame(dict(A=[1])) df.add_prefix('%') ``` #### Problem description Current implementation uses old style string formatting and breaks when passing a percent sign #### Expected Output ``` %A 0 1 ``` #### Output of ``pd.show_versions()`` <details> [paste the output of ``pd.show_versions()`` here below this line] INSTALLED VERSIONS ------------------ commit: None python: 3.6.0.final.0 python-bits: 64 OS: Darwin OS-release: 16.6.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 pandas: 0.20.3 pytest: 3.0.5 pip: 9.0.1 setuptools: 36.2.0 Cython: 0.25.2 numpy: 1.13.1 scipy: 0.18.1 xarray: 0.9.5 IPython: 5.1.0 sphinx: 1.5.1 patsy: 0.4.1 dateutil: 2.6.1 pytz: 2017.2 blosc: None bottleneck: 1.2.0 tables: 3.3.0 numexpr: 2.6.1 feather: 0.4.0 matplotlib: 2.0.0 openpyxl: 2.4.1 xlrd: 1.0.0 xlwt: 1.2.0 xlsxwriter: 0.9.6 lxml: 3.7.2 bs4: 4.5.3 html5lib: 0.9999999 sqlalchemy: 1.1.5 pymysql: None psycopg2: None jinja2: 2.9.4 s3fs: None pandas_gbq: None pandas_datareader: 0.4.0 </details>