Creating a dictionary with a path name and SHA-256 hash

Question

The purpose is just to create a dictionary with a path name, along with the file's SHA-256 hash.

I'm very new to Python, and have a feeling that there's a much better way to implement the following code. It works, I'd just like to clean it up a bit. fnamelst = [r'C:\file1.txt', r'C:\file2.txt']

[fname.replace('\\', '\\\\') for fname in fnamelst]
diction = [{fname: hashlib.sha256(open(fname, 'rb').read()).digest()} for fname in fnamelst]
for iter in range(0,len(fnamelst)):
 dic2 = {fnamelst[iter]: hashlib.sha256(open(fnamelst[iter], 'rb').read()).digest()}

• kirelagin: Why are you replacing slashes??
• kirelagin: Well, you've created the dictionary twice. What's the question?
• tobias_k: Note that the for loop will overwrite dic2 each time, instead of extending it.

Answer 1

In your code, you show two ways to create your dictionary, but both are somewhat flawed:

• diction will be a list of dictionaries, each holding just one entry
• dic2 will get overwritten in each iteration of the loop, and will finally hold only one dictionary, again with only one element.

Instead, try this:

diction = dict([ (fname, hashlib.sha256(open(fname, 'rb').read()).digest())
 for fname in fnamelst ])

Or shorter, for Python 2.7 or later:

diction = { fname: hashlib.sha256(open(fname, 'rb').read()).digest()
 for fname in fnamelst }

The first one uses a list comprehension to create a list of key-value tuples, and then uses the dict function to create a single dictionary from that list. The second one does the same, using a dict comprehension.

Answer 2

In python, for iter in range(0,len(container)): is pretty much always a bad pattern.

Here, you can rewrite :

for f in fnamelst:
 dic2 = {f: hashlib.sha256(open(f, 'rb').read()).digest()}

As @tobias_k pointed out, this doesn't do much at the moment as dict2 gets overriden. In Python 2.7+ or 3, you can just use the dict comprehension directly.

Answer 3

You have some confusion about using backslahses in Python strings.

r'C:\file1.txt' is a raw string and the backslash is a backslash. r in front denotes raw.

'C:\\file1.txt' is the same string written as a normal string literal. Now the backslash has to be written as \\, because otherwise \f would be interpreted as a control character \x0c.

Doubling the backslash using replace serves no purpose here. Moreover, as tobias_k points out, the line with the replace has no effect at all because the resulting modified list is not assigned to a variable.

• tobias_k: Moreover, the line with the replace has no effect at all, as the strings in the list are immutable, and the new list is not assigned to a variable.