How to change the format of a float number?

                .xTickFormat(function (d) {
                //console.log(new Date(data[d].x));
                return d3.time.format('%x')(new Date(data[d].x))
            })
            .yTickFormat(function () {
                return d3.format(',f')
            })

var value = 3;
var n = value.tofixed(7);

var value2 = 3.30;
var n = value2.tofixed(7);

>>> df
    Age
0  24.0
1  32.0

>>> df.dtypes
Age    float64
dtype: object

>>> df.Age
0    24.0
1    32.0
Name: Age, dtype: float64

>>> df['Age'].dtype.kind
'f'

>>> df['Age'].map('{:,.2f}'.format)
0    24.00
1    32.00
Name: Age, dtype: object

>>> pd.set_option('display.float_format','{:.0f}'.format)
>>> df
   Age
0   24
1   32

>>> df.dtypes
Age    float64
dtype: object

>>> pd.set_option('display.float_format','{:.2f}'.format)
>>> df
    Age
0 24.00
1 32.00
>>> df.dtypes
Age    float64
dtype: object

>>> pd.set_option('precision', 0)
>>> df
   Age
0   24
1   32

>>> df.dtypes
Age    float64
dtype: object