title: Fit an exponential function to time-series data
body: <p>I've to fit the following exponential function to a time-series data (<a href="https://github.com/DeepaMahm/misc/blob/master/sample.txt" rel="nofollow noreferrer">data</a>).</p>
  <pre><code>$C(t)$ = $C_{\infty} (1-\exp(-\frac{t}{\tau}))$
  </code></pre>
  <p>I want to compute the time scale <code>$\tau$</code> at which <code>C(t)</code> reaches <code>$C_{\infty}$</code>. I would like to ask for suggestions on how <code>$\tau$</code> can be computed. I found an example <a href="https://stackoverflow.com/questions/33186740/fitting-exponential-function-through-two-data-points-with-scipy-curve-fit">here</a> that use curve fitting. But I am not sure how to use <code>curve_fit</code> library in <code>scipy</code> to set up the problem described above.</p>