I would like to find a string of certain length - example 7 characters. The string must only contain uppercase letters and numbers. I have ideas to: read the file line by line...

I am unsure the best practice here- read the whole file in one block or read the file line by line using a loop? Do you have to use a loop to read the file line by line?

```py
# read lines in text file
filetoread=open("mytextfile.txt")

for lines in filetoread  # right ?
 #just an example of a given string of text (not from the file)
    characters = "D123456"
    for x in characters:
        if x == "D":
            print ("found letter", x)

```

But in my scenario I do not know what characters will be present in my 7 character length string so I can't search for "D" obviously.

So I have ideas I need to read the file, check for a string of length 7 (I am unsure how to handle stuff in the file like this:

line 1: My path = "7characters" (so basically finding even substrings that would qualify of 7 characters which contain uppercase and numeric

I dont know, this is simple, but yet I don't think i am understanding the basic logic behind it.