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Python Path and Subprocess (useful for scripting)

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We want to be able to:

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  • read/write files
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  • launch executables
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  • generate input
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  • parse ouput
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  • make graphs of publication quality
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  • post-treatment: curve fit, vector manipulation...
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Selected python scripting tools

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Manipulating filenames

import os
+path, name = os.path.split('/tmp/test.plot')
+basename, ext = os.path.splitext(name)
+print('path ' + path)
+print('name ' + name)
+print('basename ' + basename)
+print('ext ' + ext)
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How to list all files in a directory

import os
+for fname in os.listdir('/tmp'):
+    print(fname)
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list only files of a given extension

import os
+for fname in os.listdir('/tmp'):
+    name,ext = os.path.splitext(fname)
+    if not ext == '.txt':
+        continue
+    print('name ' + name)
+    print('ext ' + ext)
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construct filenames with other files and a different path

import os
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+new_path = '/newpath'
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+for fname in os.listdir('/tmp'):
+    basename = os.path.basename(fname)
+    new_file = os.path.join(new_path, basename)
+    print(new_file)
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execute other programs: Subprocess module

import subprocess
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Launching another program is simply done by the call function

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res = subprocess.call(['ls', '-trlh'])
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The output is sent to screen.

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Saving output into a file

import subprocess
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+outfile = open('out.txt', 'w')
+res = subprocess.call(['ls', '-trlh'], stdout=outfile)
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Saving output into a string

import subprocess
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+process = subprocess.Popen(["ls", "-trlh"], stdout=subprocess.PIPE)
+out, err = process.communicate()
+print (out.decode)
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Exploiting return code

import subprocess
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+process = subprocess.Popen(["ls", "-trlh"], stdout=subprocess.PIPE)
+out, err = process.communicate()
+ret = process.ret
+if ret != 0:
+    print('Failed')
+else:
+    print('return code: {0}'.format(ret))
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