Using python extract from list of string - python-3.x

Question

I have list of string from which i want to extract channel number value with low SIG value.
Below is mt list name "Outlines"
Flags: A - active, P - privacy, R - routeros-network, N - nstreme, T - tdma,
W - wds, B - bridge
ADDRESS SSID CHANNEL SIG NF SNR RADIO-... ROUTER...
AP 20:B5:C6:F1:B6:B0 INAPHDBD... 5815/2... -78 -60 -18
52:4F:54:43:4F:44 P2MPRWXX... 5835/20/a -80 -102 22
A 52:41:44:57:49:4E 5835/20/a -86 -102 16
APR B 4C:5E:0C:BF:EE:6E iBw 5865/2... -75 -102 27 4C5E0C... 6.38.5
A 00:19:70:2C:FD:82 TR6SL5 5835/20/a -86 -102 16
20:B5:C6:F0:E6:F7 5855/20/a -58 -103 45
Below is the code i tried, but didnt know how i can iterate when line starts without blank or any other random value.
RSSI = ''
Myindex = [l for l, elem in enumerate (outlines) if 'AP' in elem]
#Myindex = [elem for elem in outlines if 'AP' in elem]
#RSSI =int('nan')
for ind in Myindex:
newchannel = " ".join(outlines[ind].split()).split(' ')[3]
newRSSI = " ".join(outlines[ind].split()).split(' ')[4]
if RSSI < newRSSI or RSSI == '':
RSSI =newRSSI
channel = newchannel.split('/')[0]
print(channel)

Answer 1

You can get the positions in each line you need to parse from the line that contains 'SIG' and 'CHANNEL'.
You can loop all lines, extract the positions and convert the SIG to a number and put it into a dictionary of lists of CHANNELS (if 2 have the same SIG and both are lowest).
You can proceed to work with the dictionary data:
t = """Flags: A - active, P - privacy, R - routeros-network, N - nstreme, T - tdma,
W - wds, B - bridge
ADDRESS SSID CHANNEL SIG NF SNR RADIO-... ROUTER...
AP 20:B5:C6:F1:B6:B0 INAPHDBD... 5815/2... -78 -60 -18
52:4F:54:43:4F:44 P2MPRWXX... 5835/20/a -80 -102 22
A 52:41:44:57:49:4E 5835/20/a -86 -102 16
APR B 4C:5E:0C:BF:EE:6E iBw 5865/2... -75 -102 27 4C5E0C... 6.38.5
A 00:19:70:2C:FD:82 TR6SL5 5835/20/a -86 -102 16
20:B5:C6:F0:E6:F7 5855/20/a -58 -103 45
"""
sigstart = 0
channelstart = 0
data = {}
for line in t.split("\n"):
# find position of SIG and CHANNEL, ignore everything until we have that
if sigstart == 0:
try:
sigstart = line.index("SIG")
channelstart = line.index("CHANNEL")
except ValueError:
pass
continue
# parse line if long enough and has AP in it
if len(line)>= sigstart+3 and "AP" in line:
sig = int(line[sigstart:sigstart+3].strip())
channel = line[channelstart:sigstart].strip()
# add to dictionary - could use defaultdict if perfomance is an issue
# but for the example this works just fine
data.setdefault(sig,[]).append(channel)
# output all parsed data, sorted:
for sig,channel in sorted(data.items(), key = lambda x:x[0]):
print(sig, ', '.join(c.split("/")[0] for c in channel))
Output:
-78 5815 # lowerst, only 1 item
-75 5865
The very lowest would be sorted(data.items(), key = lambda x:x[0])[0].

Answer 2

I figure out to extract the channel value having lowest SIG value using regex, regex are very power to use specially for a nasty data(list of strings).
i used regex101 . com which makes life easier. below is the code i tried.
import re
outlines = """
Flags: A - active, P - privacy, R - routeros-network, N - nstreme, T - tdma,
W - wds, B - bridge
ADDRESS SSID CHANNEL SIG NF SNR RADIO-... ROUTER...
AP 20:b5:C6:F1:B6:B0 INAPHDBD... 5815/2... -78 -60 -18
52:4F:54:43:4F:44 P2MPRWXX... 5835/20/a -80 -102 22
A 52:41:44:57:49:4E 5835/20/a -86 -102 16
APR B 4C:5E:0C:BF:EE:6E iBw 5865/2... -75 -102 27 4C5E0C... 6.38.5
A 00:19:70:2C:FD:82 TR6SL5 5835/20/a -86 -102 16
20:b5:C6:F0:E6:F7 5855/20/a -58 -103 45
"""
regex = ".* ([0-9]+)\/[^ ]* ([-+0-9]*)[ ,]*"
oldsig =''
if __name__ == '__main__':
​
for line in outlines:
s = re.search(regex, line.replace('\r\n',''))
​
if s:
channel = s.group(1)
sig = s.group(2)
if oldsig < sig or oldsig=='':
oldsig = sig
nchannel1 = channel
print(nchannel1)
Which gives output
5835