matplot.axis() range question

When I run the script below, the range tuple is [0.0, 1.0,

    > 0.0, 1.0]

    > but the data has an actual range more like [ 0, 6.8, 0,
    > 1], the plot looks correct, which is good, but the range
    > tuple is wrong. It seems to work fine with simple data
    > examples but breaks with this data..

    > This is with Matplotlib v0.54.2

It works under 0.63 - it prints

[0.0, 1.0, 1.0, 7.0]

JDH