Try explicitly specifying the properties you want:
plt.plot(range(10),range(10),marker='o',color='b',linestyle='-')
the compact style is nice for interactive stuff, but I find using the keyword arguments makes the code more readable and makes it possible to loop control how the line properties are cycled through when plotting more than one curve on the same graph.
What is dictionary[key]
in your code? If it is a scalar then it will make 10 separate lines of length one. I think you may want to really do
plt.plot(np.arange(10),np.ones(10)*dictionary[key],marker='o',color='b',linestyle='-')
or
plt.plot(range(10),[dictionary[key]]*10,marker='o',color='b',linestyle='-')
depending on if you are using numpy or not.