Why is this Variable Losing its Value?-CodePudding

Basically, my sample dataset looks like the following:

Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA

I am trying to group every 3 lines together. So each 3 lines of the data set are related (I.e the PC's IP is 10.0.0.1 and is in Denver, the next device is a thin client in Seattle and so on)

My goal is to have Python put each of these 3 values into their own variables, so that later on in the script (omitted from my code below for brevity), I can pass them to a CSV.

My problem is that one of the variables is losing its value in the if i == 3: block.

Take a look at the following code to see an example of the issue:

output = """
Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA

 """

i = 0
output = output.split("\n")

for line in output:
    if "PC" in line:
        machine = line[-3:-1]

    if "Thin Client" in line:
        machine = line[-11:-1]

    if "IP Address" in line:
        address = line[-8:-1]

    if "Location" in line:        
        location = line[-12:-1]
        print(location)

    i = i   1
    if i == 3:
        print(machine, address, location)

Traceback (most recent call last):
  File "pytest.py", line 37, in <module>
    print(machine, address, location) 
NameError: name 'location' is not defined

Python is telling me that the location variable isn't defined, but I don't see how that's true because it was defined on the third iteration of the for loop before it was passed off to the print statement.

I can actually prove it's being defined with the following code:

output = """
Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA

 """

output = output.split("\n")

for line in output:
    if "PC" in line:
        machine = line[-3:-1]

    if "Thin Client" in line:
        machine = line[-11:-1]

    if "IP Address" in line:
        address = line[-8:-1]

    if "Location" in line:
        location = line[-12:-1]
        print(location)

Output:

Denver,US
Seattle, US

I am really lost here. Does anyone have any ideas as to what might be causing this? Or have any suggestions on how to do this in a better way?

CodePudding user response：

Counting lines is the wrong answer. If you want an output after "Location", then do the output when you get "Location". Also, remember that when you say

output = """
xxx
"""

That has a newline at the beginning, and an extra newline at the end. To eliminate those, you need to use a backslash:

output = """\
xxx"""

It's better to be able to ignore blank lines, like this does.

output = """
Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA
"""
for line in output.splitlines():
    parts = line.split(': ')
    if parts[0] == 'Machine Type':
        machine = parts[1]
    elif parts[0] == "IP Address":
        address = parts[1]
    elif parts[0] == "Location":
        location = parts[1]
        print(machine, address, location)

Output:

PC, 10.0.0.1, Denver,USA
Thin Client, 10.0.0.2, Seattle, USA

CodePudding user response：

import re

output = """
Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA
"""

ids = ['Machine Type', 'IP Address', 'Location']
values = []
for id in ids:
    values.append([x.split(': ')[1] for x in re.findall(f"({id}:.*)\n", output)])

for value in zip(*values):
    print(*value)

Output:

PC, 10.0.0.1, Denver,USA
Thin Client, 10.0.0.2, Seattle, USA

CodePudding user response：

The code you've written is very vulnerable to breakage if the formatting isn't exactly as expected -- a blank line, stray whitespace, etc can easily throw it off. Since you're using the line number (i) to decide whether or not location has been defined, a blank line will mess you up, as will reordering the data, adding another line, etc.

Here's an approach that aims to just turn your format (as far as I can infer it) into a generic list of dictionaries rather than assigning individual pieces of data to named variables:

output = """
Machine Type: PC,
IP Address: 10.0.0.1,
Location: Denver,USA
Machine Type: Thin Client,
IP Address: 10.0.0.2,
Location: Seattle, USA

 """

data = [{}]
for line in output.split("\n"):
    if not ":" in line:
        continue
    line = line.strip().rstrip(",")
    k, v = line.split(":")
    k = max(k.lower().strip().split(), key=len)
    if k in data[-1]:
        data.append({})
    data[-1][k] = v.strip()

This code isn't aware of any of the particular variables, or know (or care) what order they're in, but it produces your original three variables as entries in a dictionary that you can access any way you like:

print(data)
# [{'machine': 'PC', 'address': '10.0.0.1', 'location': 'Denver,USA'}, {'machine': 'Thin Client', 'address': '10.0.0.2', 'location': 'Seattle, USA'}]

for d in data:
    print(list(d.values()))
# ['PC', '10.0.0.1', 'Denver,USA']
# ['Thin Client', '10.0.0.2', 'Seattle, USA']

print([d["machine"] for d in data])
# ['PC', 'Thin Client']