def plot_alpha_returns(alpha_returns, ax=None):
if ax is None:<EOL><INDENT>ax = plt.gca()<EOL><DEDENT>ax.hist(alpha_returns, color='<STR_LIT:g>', label='<STR_LIT>')<EOL>ax.set_title('<STR_LIT>')<EOL>ax.axvline(<NUM_LIT:0>, color='<STR_LIT:k>', linestyle='<STR_LIT>', label='<STR_LIT>')<EOL>avg = alpha_returns.mean()<EOL>ax.axvline(avg, color='<STR_LIT:b>', label='<STR_LIT>'.format(avg))<EOL>configure_legend(ax)<EOL>return ax<EOL>
Plot histogram of daily multi-factor alpha returns (specific returns).

Parameters
----------
alpha_returns : pd.Series
    series of daily alpha returns indexed by datetime

ax :  matplotlib.axes.Axes
    axes on which plots are made. if None, current axes will be used

Returns
-------
ax :  matplotlib.axes.Axes