Difficulties with variable declaration in Python

Question

I have the following piece of code which I am trying to use to declare multiple variables at the same time:

for x in range(1, 15):
    for y in range(1, 87):

        strvar1 = "%s" % (x)
        strvar2 = "%s" % (y)

        with open("C:\\Python33\\NASDAQ Stock Strings\\NASDAQ_Config_File_" + str(strvar1) + "_" + str(strvar2) + ".txt", "r") as myurls:
            myurls2_x_y = myurls.read().replace('\n', '')

When i added a print(myurls2_x_y) and viewed the log the above code was opening each dynamic file path in sequence, then displaying and cleaning up the strings in the above text files as expected.

However, using this method in something like SAS (which is my main language) I was expecting each of the variable values to be retained as they have different names, i.e. i would expect to have variables myurls2_1_1, myurls2_1_2, myurls2_1_3 etc all declared.

The idea then is to pass them through a URL = declaration within some concurrent.futures Python code that I have so that I can submit multiple URLS at once.

All that works fine apart from when the script comes to resolve the variables dynamically generated it gets to the first one, myurls2_1_1 and says that it isn't defined when it is.

Any ideas why that might be?

Thanks

Have you tried using lists? You could use myurls2[x][y] with nested lists. — grc
– grc, Commented Mar 15, 2014 at 14:04
im a bit sketchy around lists and dictionaries at the minute as to how to code them. actually one thing i hadn't thought of is that I will need to define this variables globally I think. — user3043997
– user3043997, Commented Mar 15, 2014 at 14:05

Mark Tolonen · Accepted Answer · 2014-03-15 14:34:50Z

1

One way is to use a dictionary using an x,y tuple as the key:

myurls = {}
for x in range(1, 15):
    for y in range(1, 87):
        with open("C:\\Python33\\NASDAQ Stock Strings\\NASDAQ_Config_File_{}_{}.txt".format(x,y),"r") as f:
            myurls[x,y] = f.read().replace('\n', '')

Here's a example that I can run without your files to demonstrate lookup:

myurls = {}

TEMPLATE = r'C:\Python33\NASDAQ Stock Strings\NASDAQ_Config_File_{}_{}.txt'

def content(filename):
    with open(filename) as f:
        return f.read().replace('\n', '')

for x in range(1, 15):
    for y in range(1, 87):
        #myurls[x,y] = content(TEMPLATE.format(x,y))
        myurls[x,y] = TEMPLATE.format(x,y)

print(myurls[1,5])

Output:

C:\Python33\NASDAQ Stock Strings\NASDAQ_Config_File_1_5.txt

edited Mar 15, 2014 at 14:34

answered Mar 15, 2014 at 14:13

Mark Tolonen

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6 Comments

user3043997 Over a year ago

Ok thanks. What is most likely to resolve this issue? Using a dictionary or globally declaring the variables? Or do I need to do both?

Mark Tolonen Over a year ago

Your issue is assuming how Python works. Python is not SAS. Defining myurls2_x_y only defines myurls2_x_y as a variable. Python will not magically create myurls2_1_1, etc. for you. Use dictionaries or lists instead and access them with myurls[x,y] (for dict) or myurls[x][y] (for lists).

user3043997 Over a year ago

Using the exact syntax in your answer i got the following error: Traceback (most recent call last): File "C:\Python33\test2.py", line 19, in <module> with open("C:\\Python33\\NASDAQ Stock Strings\\NASDAQ_Config_File_{}_{}".format(x,y),"r") as f: FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Python33\\NASDAQ Stock Strings\\NASDAQ_Config_File_1_1'

user3043997 Over a year ago

But it is definitely there.

Mark Tolonen Over a year ago

I left out the .txt. Fixing. I don't have your files so the code was untested.

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