How do I save a new graph as png with every iteration of a loop

Question

I don't know how to save a new graph png for each iteration of a loop using NetworkX. I've borrowed the code from this question: in NetworkX cannot save a graph as jpg or png file and manipulated it a bit. Below is the code:

import networkx as nx
import matplotlib.pyplot as plt

fig = plt.figure(figsize=(12,12))
ax = plt.subplot(111)
ax.set_title('Graph - Shapes', fontsize=10)

G = nx.DiGraph()
G.add_node('shape1', level=1)
G.add_node('shape2', level=2)
G.add_node('shape3', level=2)
G.add_node('shape4', level=3)
G.add_edge('shape1', 'shape2')
G.add_edge('shape1', 'shape3')
G.add_edge('shape3', 'shape4')
pos = nx.spring_layout(G)
n = 0
colorses = ['yellow', 'red', 'blue', 'green']
while n < len(colorses):
    nx.draw(G, pos, node_size=1500, node_color=colorses[n], font_size=8, font_weight='bold')
    plt.tight_layout()
    # plt.show()
    plt.savefig("Graph.png", format="PNG")
    n += 1

Ideally I would like to have four images each one with different color nodes. Let me know if you need any more information. Thanks!

um... what if you change the filename each iteration, so make `"Graph.png"` dependant of `n`, like `plt.savefig("Graph{}.png".format(n), format="PNG")`? — Tadhg McDonald-Jensen, Aug 11 '16 at 19:22

score 3 · Accepted Answer · answered Aug 11 '16 at 19:33

Just change the name of the output file

while n < len(colorses):
    nx.draw(G, pos, node_size=1500, node_color=colorses[n], font_size=8, font_weight='bold')
    plt.tight_layout()
    # plt.show()
    plt.savefig("Graph" + str(n) +".png", format="PNG")
    n += 1

You should use more descriptive names though. Maybe instead of n, you could refer to a time

    plt.savefig("Graph" + str(datetime.datetime.now()) +".png", format="PNG")

That isn't great, since the string will have whitespace, but you can tweak it beforehand

score 1 · Answer 2 · answered Aug 11 '16 at 19:33

First suggestion, accessing the colors by their index values is not "Pythonic". Instead, use a for loop:

for color in colors:
    print(color)

Your code is overwriting Graph.png on each iteration of the loop. To save a new file for each iteration, simply rename the output file on each iteration. One way to do this is by using the format() and enumerate() functions:

import networkx as nx                                                                                             
import matplotlib.pyplot as plt                                             

fig = plt.figure(figsize=(12,12))                                           
ax = plt.subplot(111)                                                       
ax.set_title('Graph - Shapes', fontsize=10)                                 

G = nx.DiGraph()                                                            
G.add_node('shape1', level=1)                                               
G.add_node('shape2', level=2)                                               
G.add_node('shape3', level=2)                                               
G.add_node('shape4', level=3)                                               
G.add_edge('shape1', 'shape2')                                              
G.add_edge('shape1', 'shape3')                                              
G.add_edge('shape3', 'shape4')                                              
pos = nx.spring_layout(G)                                                   
colors = ['yellow', 'red', 'blue', 'green']                                 
for i, color in enumerate(colors):                                          
    nx.draw(G, pos, node_size=1500, node_color=color, font_size=8, font_weight='bold')
    plt.tight_layout()                                                      
    plt.savefig('Graph_{}.png'.format(i), format="PNG")

score 1 · Answer 3 · answered Feb 02 '19 at 17:29

By the way, I just used this method and I added a step futher for my labels to be from my filename. I hope it helps someone.

    files = glob.glob(folder+'\\'+'*.csv', recursive=False)
    for file in files:
        df1=pd.read_csv(file,header=1,sep=',')
        nslice = (sum(1 for line in open(file))-1)/3
        base = print(os.path.splitext(os.path.basename(file))[0])
        fig = plt.figure()
        ax = plt.subplot(111)
        c = ax.plot(df1.iloc[0:int(nslice)-1,[22]],df1.iloc[0:int(nslice)-1,[4]],label='Cuticle')
        t = ax.plot(df1.iloc[int(nslice):(int(nslice)-1)*2,[22]],df1.iloc[int(nslice):(int(nslice)-1)*2,[4]],label='Tissue')
        p = ax.plot(df1.iloc[int(nslice)*2:(int(nslice)-1)*3,[22]],df1.iloc[int(nslice)*2:(int(nslice)-1)*3,[4]],label='Phenanthrene')
        title_obj = plt.title(base)
        plt.xlabel("Slice #")
        plt.ylabel("Avg MGV")
        ax.legend()
        plt.savefig('plot'+str(os.path.splitext(os.path.basename(file))[0])+'.png')
        plt.show()
        plt.close('all')

Peace

How do I save a new graph as png with every iteration of a loop

3 Answers3

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