import re

df = pd.DataFrame(["percent: 71.3456789%"],columns=["pct"])

>>> df
                    pct
0  percent: 71.3456789%

repl = lambda m: m.groups(0)[0] + str(round(float(m.groups(0)[1]),0)) + m.groups(0)[2]

simple_decimal = re.compile(r'(percent: )(d*.d+)(%)')

>>> df.pct.str.replace(simple_decimal,repl,regex=True)
0    percent: 71.0%