1

Goal is to switch an exhaust fan at an outside data-logging station at a solar power station. The data-collection program is written in Python under Raspbian.

For reading CPU temp at a command line, there is the vcgencmd command.

Example in bash:

echo "The CPU is at $(vcgencmd measure_temp) degrees."

The CPU is at temp=39.2'C degrees.

as the command returns the string "temp=39.2'C"

I've never personally seen this fail, although I know there is a question about that point.

vcgencmd measure_temp doesn't always work

Meanwhile, I would like to obtain the CPU temp in Python.

Back to the Goal: the fans are controlled by PiGPIO calls, and during data-logging I keep my external system calls to the minimum (ie., there aren't any other than Python file I/O). Also, it would be much preferable to get the answer as a simple floating-point value than to extract it from a return strung.


The question is: How to directly get CPU temp in Python?

3

First, set up Python:

pip install setuptools
sudo pip install git+https://github.com/nicmd/vcgencmd.git

Handy bash script cputemp

(shebang)/usr/bin/python
import vcgencmd
CPUc=vcgencmd.measure_temp()
print str(CPUc)

chmod +x cputemp
sudo cp cputemp /usr/bin

Example use in bash:

echo "The CPU is at $(cputemp) degrees C."

The CPU is at 39.6 degrees C.

Short and to the point, and in the floating data format for comparisons within the Python program..

  • Good answer. Is this any faster or slower than os.popen('vcgencme measure_temp')? – Elliott B Jul 23 '18 at 2:51
3

For those coming here from Google. You can get Raspberry CPU temp in Python using gpiozero package.

 pip install gpiozero

Create your temp.py

from gpiozero import CPUTemperature

cpu = CPUTemperature()
print(cpu.temperature)

Output :

$ python temp.py
56.92
2

"On Stretch there is no vcgencmd command at all."

So what is

 vcgencmd commands
commands="vcos, ap_output_control, ap_output_post_processing, vchi_test_init, vchi_test_exit, vctest_memmap, vctest_start, vctest_stop, vctest_set, vctest_get, pm_set_policy, pm_get_status, pm_show_stats, pm_start_logging, pm_stop_logging, version, commands, set_vll_dir, set_backlight, set_logging, get_lcd_info, arbiter, cache_flush, otp_dump, test_result, codec_enabled, get_camera, get_mem, measure_clock, measure_volts, scaling_kernel, scaling_sharpness, get_hvs_asserts, get_throttled, measure_temp, get_config, hdmi_ntsc_freqs, hdmi_adjust_clock, hdmi_status_show, hvs_update_fields, pwm_speedup, force_audio, hdmi_stream_channels, hdmi_channel_map, display_power, read_ring_osc, memtest, dispmanx_list, get_rsts, schmoo, render_bar, disk_notify, inuse_notify, sus_suspend, sus_status, sus_is_enabled, sus_stop_test_thread, egl_platform_switch, mem_validate, mem_oom, mem_reloc_stats, hdmi_cvt, hdmi_timings, file"

 vcgencmd measure_temp
temp=42.9'C
  • You are correct. Changing Q&A to focus on Python. – SDsolar Jun 28 '18 at 6:44
1

Related to the other answers:

Using the nice answer to Less ugly yet reliable way to find this floating-point value embedded within a string without padding?:

import re, commands

def check_CPU_temp():
    temp = None
    err, msg = commands.getstatusoutput('vcgencmd measure_temp')
    if not err:
        m = re.search(r'-?\d\.?\d*', msg)   # https://stackoverflow.com/a/49563120/3904031
        try:
            temp = float(m.group())
        except:
            pass
    return temp, msg

temp, msg = check_CPU_temp()

print "temperature (" + u'\xb0' + "C): ", temp
print "full message:    ", msg

which returns both a floating point value and the original message in which it is contained.

temperature (°C):  49.0
full message:     temp=49.9'C
  • 1
    note commands is python2, it has been replaced with subprocess, though there are other py2-specific things in here too. – tedder42 Sep 7 '18 at 21:28
  • @tedder42 thanks for that! I'll try tend to this soon, but you are welcome to edit it yourself or post a new answer if you feel so inclined. I'm aware that the time is coming and 2.7 will no longer be supported and us 2.7ers need to port ourselves over, I've just been procrastinating... which reminds me that I hadn't accepted your Space answer yet... done! – uhoh Sep 8 '18 at 0:05
  • I was/am still reticent to change it this dramatically. I think it's okay to just leave it, especially because there's no canonical way to do it anyhow. – tedder42 Sep 9 '18 at 1:16
0

It has already been answered and accepted but I see that no one has brought up this alternative that doesn't depend on running a command but rather on reading from a file. /sys/class/thermal/thermal_zone0/temp. This file holds the temperature in micro-degrees Celsius.

$ vcgencmd measure_temp && cat /sys/class/thermal/thermal_zone0/temp
temp=47.8'C
47774

So, open the file and read the content. No need to do string processing.

0

On the RPi Foundation site, there is a guide on how to make a temperature log. In it are instructions on the GPIO Python library built into Raspbian. https://projects.raspberrypi.org/en/projects/temperature-log

  • It goes back to same as answer given by @hg8 i.e. pip install gpiozero and from gpiozero import CPUTemperature to get the temp. – Adarsha Sep 5 at 2:33

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