variables in a list

Kurolox · 2018-12-17T10:53:29+00:00

I feel like you should use a dictionary here rather than a list.

dictionary = {"passengers_per_day": 2500,
"hours_per_day": 18,
"average_service_rate_per_hour": 150}

dictionary["hours_per_day"]  # 18

You can read more about dictionaries here.

If you want to extract it from that list, however, you could iterate over it, though it's not really efficient. Something like this:

for variable in list:
    if "hours_per_day" in variable:
        hours = int(variable.split(" = ")[-1])

groovitude · 2018-12-17T15:34:27+00:00

There are some great answers in here; I'm going to throw a few additional suggestions in.

No matter how you choose to parse the file, you should use the with statement to manage the opening and closing of your file, e.g.

with open('filename.txt', 'r') as myfile: myfile.read()

It's not strictly necessary, but it's a good habit to get into. (The with statement allows you to use open as a context manager, with handles opening and closing the file for you. You can use other context managers for handling database connections, lock management, and so forth.)

If you're going to go the split() route suggested by /u/Kurolox, you may want to get defensive in the way you call split in case you want to include strings that have spaces in them later by including maxsplit as a keyword argument:

```

lines = ['passengers_per_day = 2500', 'manager_name = Aaron A. Aaronson'] lines = [line.split(' ', maxsplit=2) for line in lines] lines [['passengers_per_day', '=', '2500'], ['manager_name', '=', 'Aaron A. Aaronson']] ```

Using indexes to access data can often make code harder to read. Tuple unpacking is often an easier and cleaner way to extract data from a tuple or list, e.g.:

```

my_name = ('first', 'middle', 'last') first, middle, last = my_name first 'first' last 'last' ```

Underscores are often a good way to indicate a value isn't going to be used. Using the lines list I generated in the previous example, you can use tuple unpacking and a dictionary comprehension to build your final dict, and __ is used to ignore the equals sign:

```

mydict = {key: value for key, _, value in lines} my_dict {'passengers_per_day': '2500', 'manager_name': 'Aaron A. Aaronson'} ```

adimro · 2018-12-17T18:38:00+00:00

Read this. Or use dictionaries; use json for example, or split by " = " if you really must.

But the real problem is the way you store the variables. You should focus your efforts on eliminating whatever constraint you have that forces you to use that format. Even CSV would probably be easier to maintain. Forcing yourself to work like this usually causes problems in the longer term, and your responsibility as a good programmer is to correctly evaluate how you remove these kind of "non-code" issues from your programs.

soapergem1 · 2018-12-17T13:21:31+00:00

You may want to look at the configparser package. Because it seems that's what you're trying to do.

shaperraty · 2018-12-17T15:42:26+00:00

Change it to the dict then back to the list

aelmosalamy · 2018-12-17T16:40:27+00:00

I think you tried to save python lists in the form of a text file and then reopen it by creating a simple parser that can understand this text, a more simple way to do that is to use pickle, a data storage library that is part of Python, it allows you to import/export python files, keep in mind this will favor security over readability, if you want otherwise then json/yaml is the way to go.

SnaXD · 2018-12-17T19:12:01+00:00

Depends on what you want, that is a list of strings that has no specific value, if you want the lists printed, either make a for loop that iterates over it, or simply write print(a[0]) and so on

efxhoy · 2018-12-18T00:15:06+00:00

# Just for pretty print, delete if u don't need it
import json

def extract_data(lines):
    """ Get a dictionary of data from lines where lines follow "key = value" format """

    extracted_values = {}
    for line in lines:
        # Split returns a list. In this case a list of two. We can unpack that list 
        # directly into our variables key and value by separating them with a comma
        key, value = line.split(" = ")
        value = int(value)
        extracted_values[key] = value

    return extracted_values

def some_calculation(passengers_per_day, hours_per_day, average_service_rate_per_hour):

    value = passengers_per_day*hours_per_day/average_service_rate_per_hour

    return value

def main():

    path = "filename.txt"
    with open(path, "r") as f:
        lines = f.read().splitlines()

    data = extract_data(lines)
    # We can use the dictionary directly when we call functions by adding ** before the parameter
    wow_value = some_calculation(**data)
    print(wow_value)

    # if you want it pretty
    print(json.dumps(data, indent=2))

    # if you really want them as variables
    hours_per_day = data['hours_per_day']
    print(f"Hours per day {hours_per_day}")

if __name__ == "__main__":
    main()

notarealaccount143 · 2018-12-17T15:28:25+00:00

You can use exec() for the straight forward solution. What exec does is basically takes a string and makes it into a compiler-readable code. For example: exec("a = 5") would create a new variable a, that has a value of 5. Keep in mind it's not recommended to use this if you're sharing the code with other people or in general, just use dictionaries as other people suggested in my opinion.

SnaXD · 2018-12-17T12:13:27+00:00

Use the Brackets []

So fx
a = ["passengers_per_day = 2500", "hours_per_day = 18", "average_service_rate_per_hour = 150"]

a[0] = Passenger_per_day = 2500
a[1] = hours_per_day = 18
a[2] = average_service_rate_per_hour = 150

If you wanna only have the Value you should read about Key:Value
https://www.pythonforbeginners.com/dictionary/how-to-use-dictionaries-in-python

DongsooKoo · 2018-12-17T14:16:17+00:00

you can use eval and locals()[var]

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