I'm reading the Wi-Fi connection of my Raspberry Pi, using the iwgetid command.
The output is:
wlan0 ESSID:"iPhone"
I wrote the following lines in a Python script:
import os
print(os.system("iwgetid"))
print(type(os.system("iwgetid")))
The output I got was:
0
<type 'int'>
Why is print(os.system("iwgetid") giving me 0 when it's a string?
As quoted from here:
os.system() just runs the process, it doesn't capture the output:
If command generates any output, it will be sent to the interpreter
standard output stream. The return value is the exit code of the
process:
On Unix, the return value is the exit status of the process encoded in
the format specified for wait().
To get the output from the Terminal command, use the subprocess module and the command subprocess.check_output instead of os.system.
Related
I am trying to send a file via serial port. I tried sending picocom commands in a bash script. However the device writes out a menu of options. When it gets to the file transfer step - it writes out 'C' until a file is sent, after which it does the handshake and proceeds with the transfer. With the script I am not able to send the keystrokes 'C-a' and 'C-s' to get the '*** file:' prompt of picocom. I can do it manually. I even tried a combination of bash and python and pyautogui for the keystrokes, bash echo command to send the hex version of the keystrokes. I even tried sending 'sz' commands through the script and stty. All of these attempts were unsuccessful.
So I switched to python, and tried the xmodem library in python. I am supposed to use ymodem. I thought the 'YMODEM batch transmission session' in the library would do the job. The modem.send command always errors out with the file not being sent.
Read Byte: b'C'
Put Byte: 133
Read Byte: b'C'
send error: expected ACK; got b'C' for block 1
Put Byte: 133
Read Byte: b'C'
send error: expected ACK; got b'C' for block 1
How can i get around this?
Finally ended up using a combination of python and bash - python for serial communication and for parsing the file names of the binaries, and, bash stty and sb commands for transferring the binaries.
I am using a third-party C++ program to generate intermediate results for the python program that I am working on. The terminal command that I use looks like follows, and it works fine.
./ukb/src/ukb_wsd --ppr_w2w -K ukb/scripts/wn30g.bin -D ukb/scripts/wn30_dict.txt ../data/glass_ukb_input2.txt > ../data/glass_ukb_output2w2.txt
If I break it down into smaller pieces:
./ukb/src/ukb_wsd - executable program
--ppr_w2w - one of the options/switches
-K ukb/scripts/wn30g.bin - parameter K indicates that the next item is a file (network file)
-D ukb/scripts/wn30_dict.txt - parameter D indicate that the next item is a file (dictionary file)
../data/glass_ukb_input2.txt - input file
> - shell command to write the output to a file
../data/glass_ukb_output2w2.txt - output file
The above works fine for one instance. I am trying to do this for around 70000 items (input files). So found a way by using the subprocess module in Python. The body of the python function that I created looks like this.
with open('../data/glass_ukb_input2.txt', 'r') as input, open('../data/glass_ukb_output2w2w_subproc.txt', 'w') as output:
subprocess.run(['./ukb/src/ukb_wsd', '--ppr_w2w', '-K', 'ukb/scripts/wn30g.bin', '-D', 'ukb/scripts/wn30_dict.txt'],
stdin=input,
stdout=output)
This error is no longer there
When I execute the function, it gives an error as follows:
...
STDOUT = subprocess.STDOUT
AttributeError: module 'subprocess' has no attribute 'STDOUT'
Can anyone shed some light about solving this problem.
EDIT
The error was due to a file named subprocess.py in the source dir which masked Python's subprocess file. Once it was removed no error.
But the program could not identify the input file given in stdin. I am thinking it has to do with having 3 input files. Is there a way to provide more than one input file?
EDIT 2
This problem is now solved with the current approach:
subprocess.run('./ukb/src/ukb_wsd --ppr_w2w -K ukb/scripts/wn30g.bin -D ukb/scripts/wn30_dict.txt ../data/glass_ukb_input2.txt > ../data/glass_ukb_output2w2w_subproc.txt',shell=True)
My Python 3.7.1 script generates a fasta file called
pRNA.sites.fasta
Within the same script, I call following system command:
cmd = "weblogo -A DNA < pRNA.sites.fasta > OUT.eps"
os.system(cmd)
print(cmd) #for debugging
I am getting the following error message and debugging message on the command line.
Error: Please provide a multiple sequence alignment
weblogo -A DNA < pRNA.sites.fasta > OUT.eps
"OUT.eps" file is generated but it's emtpy. On the other hand, if I run the following 'weblogo' command from the command line, It works just find. I get proper OUT.eps file.
$ weblogo -A DNA<pRNA.sites.fasta>OUT.eps
I am guessing my syntax for os.system call is wrong. Can you tell me what is wrong with it? Thanks.
Never mind. It turned out to be that I was not closing my file, "pRNA.sites.fasta" before I make system call that uses this file.
I want to pipe data via stdin to a Python script for onwards processing. The command is:
tail -f /home/pi/ALL.TXT | python3 ./logcheck.py
And the Python code is:
import sys
while 1:
if (sys.stdin.isatty()):
for line in sys.stdin:
print(line)
I want the code to continuously watch stdin and then process each row when received. The tail command is working when run on its own but the python script never outputs anything.
Checking isatty() it appears to always return False?
Help!
A TTY is when you use your regular terminal - as in opening up a python in your shell, and typing
BASH>python
>>>from sys import stdin
>>>stdin.isatty() #True
In your case the standard input is coming from something which is not a tty. Just add a not in the if statement.
This is a simple code that logs into a linux box, and execute a grep to a resource on the box. I just need to be able to view the output of the command I execute, but nothing is returned. Code doesn't report any error but the desired output is not written.
Below is the code:
import socket
import re
import paramiko
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('linux_box', port=22, username='abc', password='xyz')
stdin, stdout, stderr = ssh.exec_command('grep xyz *.set')
output2 = stdout.readlines()
type(output2)
This is the output I get:
C:\Python34\python.exe C:/Python34/Paramiko.py
Process finished with exit code 0
You never actually print anything to standard output.
Changing last line to print(output2) should print value correctly.
Your code was likely based on interactive Python shell experiments, where return value of last executed command is printed to standard output implicitly. In non-interactive mode such behavior does not occur. That's why you need to use print function explicitly.