How to loop through a list of strings in Python

Question

I'm a bit new to Python and I am trying to simplify my existing code. Right now, I have the code repeated 5 times with different strings. I'd like to have the code one time and have it run through a list of strings.

Currently what I have:

def wiScanFormat():

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    MAC = data.replace("Address:", "\nAddress, ")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(MAC)
    File.close()

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    SSID = data.replace("ESSID:", "\nESSID, ")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(SSID)
    File.close()

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    FREQ = data.replace("Frequency:", "\nFrequency, ")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(FREQ)
    File.close()

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    QUAL = data.replace("Quality", "\nQuality, ")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(QUAL)
    File.close()

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    SIG = data.replace("Signal level", "\nSignal Level, ")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(SIG)
    File.close()

What I'd like to have:

ORG = ['Address:', 'ESSID:'...etc]
NEW = ['\nAddress, ' , '\nESSID, ' , ...  etc]

and run that through:

    File = open("/home/pi/gpsMaster/WiScan.txt", "r")
    data = File.read()
    File.close()
    ID = data.replace("ORG", "NEW")
    File = open("/home/pi/gpsMaster/WiScan.txt", "w")
    File.write(ID)
    File.close()

I've tried running exactly what I put up, but it does not seem to format it the way I need to.

The output from above looks like:

Cell 46 - Address: xx:xx:xx:xx:xx:xx    ESSID:"MySSID"  Frequency:2.412 GHz (Channel 1) Quality=47/100  Signal level=48/100 Quality=47/100  Signal level=48/100

But it is supposed to look like this (And it does when I run that same block over the strings separately):

xx:xx:xx:xx:xx:xx   MySSID  5.18 GHz (Channel 36)   0.81    0.99

How should I go about looping this block of code through my list of strings? There two strings that I would need for the find and replace, old and new, so they would have to work together. These lists will be the same size, obviously, and I need them to be in the correct order. Address with address, ESSID with ESSID, etc.

Thanks in advance!

Are you genuinely opening the same file five times to perform a sequence of different edits on it, or have I misunderstood? — khelwood
– khelwood, Commented Apr 12, 2016 at 13:12
@khelwood Yes, currently I am. I'm aware this isn't the most efficient way to go about this which is why I am exploring other options edit: actually, its being open 10 times. 5 for reads, 5 for writes — sjo91190
– sjo91190, Commented Apr 12, 2016 at 13:15
1. replace only replace the first match if I remember correctly. Use re.sub instead. 2. use with open("..") as f: # do something instead of f = open("..") and f.close. 3. post your formatted example data! — knh170
– knh170, Commented Apr 12, 2016 at 13:18
@knh170: str.replace defaults to replacing all instances, not one, it takes an argument to limit replacements. Don't push people to regular expressions for simple replacement operations, this isn't Perl! :-) — ShadowRanger
– ShadowRanger, Commented Apr 12, 2016 at 13:22

acdr · Accepted Answer · 2016-04-12 13:19:00Z

1

Try something like this:

ORG = ['Address:', 'ESSID:'...etc]
NEW = ['\nAddress, ' , '\nESSID, ' , ...  etc]

File = open("/home/pi/gpsMaster/WiScan.txt", "r")
data = File.read()
File.close()
for org, new in zip(ORG, NEW):
    data = data.replace(org, new)
File = open("/home/pi/gpsMaster/WiScan.txt", "w")
File.write(data)
File.close()

(Note the way zip works: https://docs.python.org/2/library/functions.html#zip)

answered Apr 12, 2016 at 13:19

acdr

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1 Comment

sjo91190 Over a year ago

This worked perfectly and was exactly what I was looking for. Thanks! I was trying to use zip before I posted this but wasn't able to figure it out.

khelwood · Accepted Answer · 2016-04-12 13:17:03Z

If I am reading your question right, you are opening the same file, making a small alteration, saving it, and then closing it again, five times. You could just open it once, make all the alterations, and then save it. For instance, like this:

filename = "/home/pi/gpsMaster/WiScan.txt"
with open(filename, 'r') as fin:
    data = fin.read()
data = data.replace("Address:", "\nAddress, ")
data = data.replace("ESSID:", "\nESSID, ")
data = data.replace("Frequency:", "\nFrequency, ")
data = data.replace("Quality", "\nQuality, ")
data = data.replace("Signal level", "\nSignal Level, ")
with open(filename, 'w') as fout:
    fout.write(data)

If you want to use lists (ORG and NEW) for your replacements, you could do this:

with open(filename, 'r') as fin:
    data = fin.read()
for o,n in zip(ORG, NEW):
    data = data.replace(o,n)
with open(filename, 'w') as fout:
    fout.write(data)

ShadowRanger · Accepted Answer · 2016-04-12 13:18:27Z

1

Given your ORG and NEW, the simplest way to do this would be something like:

# Open once for both read and write; use with statement for guaranteed close at end of block
with open("/home/pi/gpsMaster/WiScan.txt", "r+") as f:
    data = f.read()  # Slurp file
    f.seek(0)        # Seek back to beginning of file
    # Perform all replacements
    for orig, repl in zip(ORG, NEW):
        data = data.replace(orig, repl)
    f.write(data)    # Write new data over old
    f.truncate()     # If replacement shrunk file, truncate extra

answered Apr 12, 2016 at 13:18

ShadowRanger

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Comments

jan · Accepted Answer · 2016-04-12 13:29:46Z

You could just do this:

def wiScanFormat(path = "/home/pi/gpsMaster/WiScan.txt"): 

    # List of tuples with strings to find and strings to replace with
    replacestr = [
                ("Address:", "\nAddress, "),
                ("ESSID:", "\nESSID, "),
                ("Frequency:", "\nFrequency, "),
                ("Quality", "\nQuality, "),
                ("Signal level", "\nSignal Level, ")
                ]

    with open(path, "r") as file:               # Open a file
        data = file.read()

    formated = data
    for i in replacestr:                        # Loop over each element (tuple) in the list
        formated = formated.replace(i[0], i[1]) # Replace the data

    with open(path, "w") as file:
        written = file.write(formated)          # Write the data

    return written

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