Adapted and simplified from Franck Albinet's exercises available here. Also presented by NSRC at APRICOT 2018.
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You will learn how to: access and operate device's file system; create and write a file in the flash folder; mount and use an SD card as an alternative; handle files safely using with statement; generate programmatically time stamped log file names; make your code robust and flexible with try ... except statement.
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- a LoPy or WiPy module
- a microUSB cable
- a development PC
The source code is in the src/micro-sd directoryavailable here.
Folder structure
The folder tree is the following:
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Let's explore and navigate this folder structure interactively. Connect to a Lopy via the Atom console and import . If there is a program running, use Control-C to stop it. Import the basic operating system module (os): import os.
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base = '/flash/log/acq/'
time_stamp = ''.join(['{:02d}'.format(i) for i in time.localtime()][:6])
name = base + time_stamp + 'list.csv'
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Let's unpack this second implementation:
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time.localtime() |
outputs a tuple (1970, 1, 1, 0, 21, 40, 3, 1) representing year, month, ...
- formatting integer to string with list comprehension
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['{:02d}'.format(i) for i in time.localtime()
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outputs ['1970', '01', '01', '00', '24', '05', '03', '01']
We keep only year, month, day, hour, min., sec. by slicing the list:
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['{:02d}'.format(i) for i in time.localtime()][:6]
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- last we join the list to a single string
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''.join(['{:02d}'.format(i) for i in time.localtime()][:6])
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outputs: '19700101002920'
We can now simply concatenate this substring with a prefix and suffix and that's done.
As it is a quite frequent operation, we could even encapsulate it in an helper function as below:
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def get_log_filename(prefix, suffix):
time_stamp = ''.join(['{:02d}'.format(i) for i in time.localtime()][:6])
return prefix + time_stamp + suffix |
and use it when required: get_log_filename('/flash/log/acq', 'list.csv')
Exercise
Write a script writing a file named "log.csv" in /flash/log/ folder so that:
- if the user pushes the button the pressing time and an incremented counter is saved;
- it the counter reaches 10, LED is switched on.