Histogram in Python Using matplotlib

Question

I am struggling with this really badly. There is something that I'm just not getting. I have a function, which I want to plot a histogram of a dictionary with the keys on the x-axis and the values on the y-axis, then save the file in a location specified when calling the function. What I have is:

​import matplotlib.pyplot as plt


def test(filename):
    dictionary = {0:1000, 1:20, 2:15, 3:0, 4:5}
    xmax = max(dictionary.keys())
    ymax = max(dictionary.values())
    plt.hist(dictionary,xmax)
    plt.title('Histogram Title')
    plt.xlabel('Label')
    plt.ylabel('Another Label')
    plt.axis([0, xmax, 0, ymax])
    plt.figure()
    plt.savefig(filename)

test('test_graph.svg')

I simply cannot get this to work, and I've struggled for a very long time reading other questions and documentation. Any help would be greatly appreciated. Thanks.

EDIT:

The error I have is:

File "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 343, in figure
    **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 80, in new_figure_manager
    window = Tk.Tk()
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1688, in __init__
    self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
TclError: no display name and no $DISPLAY environment variable

Solution

You are getting snarled up by the state-machine interface:

import matplotlib.pyplot as plt

def test(filename):
    dictionary = {0:1000, 1:20, 2:15, 3:0, 4:5}
    xmax = max(dictionary.keys())
    ymax = max(dictionary.values())
    plt.figure() # <- makes a new figure and sets it active (add this)
    plt.hist(dictionary,xmax) # <- finds the current active axes/figure and plots to it
    plt.title('Histogram Title') 
    plt.xlabel('Label')
    plt.ylabel('Another Label')
    plt.axis([0, xmax, 0, ymax])
    # plt.figure() # <- makes new figure and makes it active (remove this)
    plt.savefig(filename) # <- saves the currently active figure (which is empty in your code)

test('test_graph.svg')

See How can I attach a pyplot function to a figure instance? for a longer explanation of the state-machine vs OO interfaces for matplotlib.

Comments

[user2236076]

I updated to your code but I'm still getting this error: File "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 343, in figure **kwargs) File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tk‌​agg.py", line 80, in new_figure_manager window = Tk.Tk() File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1688, in init self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use) TclError: no display name and no $DISPLAY environment variable

[BrenBarn]

@user2236076: That sounds like your backend isn't set up right. You might want to ask a separate question about that.