[ Python 常見問題 ] matplotlib - Changing the “tick frequency” on x or y axis in matplotlib?

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Question 
I am trying to fix how python plots my data. 
Say 

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1. x = [0,5,9,10,15]  

and 

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1. y = [0,1,2,3,4]  

Then I would do: 

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1. matplotlib.pyplot.plot(x,y)  
2. matplotlib.pyplot.show()  

and the x axis' ticks are plotted in intervals of 5. Is there a way to make it show intervals of 1? 

How-To 
You could explicitly set where you want to tick marks with plt.xticks: 

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1. plt.xticks(np.arange(min(x), max(x)+1, 1.0))  

For example, 

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1. import numpy as np  
2. import matplotlib.pyplot as plt  
3.   
4. x = [0,5,9,10,15]  
5. y = [0,1,2,3,4]  
6. plt.plot(x,y)  
7. plt.xticks(np.arange(min(x), max(x)+1, 1.0))  
8. plt.show()  

np.arange was used rather than Python's range function just in case min(x) and max(x) are floats instead of ints. The plt.plot (or ax.plot) function will automatically set default x and y limits. If you wish to keep those limits, and just change the stepsize of the tick marks, then you could use ax.get_xlim() to discover what limits Matplotlib has already set: 

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1. start, end = ax.get_xlim()  
2. ax.xaxis.set_ticks(np.arange(start, end, stepsize))  

The default tick formatter should do a decent job rounding the tick values to a sensible number of significant digits. However, if you wish to have more control over the format, you can define your own formatter. For example, 

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1. ax.xaxis.set_major_formatter(ticker.FormatStrFormatter('%0.1f'))  

Here's a runnable example: 

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1. import numpy as np  
2. import matplotlib.pyplot as plt  
3. import matplotlib.ticker as ticker  
4.   
5. x = [0,5,9,10,15]  
6. y = [0,1,2,3,4]  
7. fig, ax = plt.subplots()  
8. ax.plot(x,y)  
9. start, end = ax.get_xlim()  
10. ax.xaxis.set_ticks(np.arange(start, end, 0.712123))  
11. ax.xaxis.set_major_formatter(ticker.FormatStrFormatter('%0.1f'))  
12. plt.show()