Iterate through dictionary of file objects and file names

[Julian Yap]

Hi all,
I'm trying to get some ideas on the best way to do this.

In this particular coding snippet, I was thinking of creating a
dictionary of file objects and file names. These would be optional
files that I could open and parse. At the end, I would easily close off
the files by iterating through the dictionary.

---< CODE FOLLOWS >---
optionalfiles = {fileAreaCode: "areacode.11", fileBuild: "build.11"}

# Try to see if optional file exists, if so, open.
try:
for key, optionalFile in optionalFiles.iteritems():
key = open(optionalFile, "r")
except IOError:
key = False

....

# Close optionally open files
for key, optionalFile in optionalFiles.iteritems():
if optionalFile:
print "Closing: %s" % optionalFile
key.close()

---< END CODE >---

My questions are:
Is this even possible in a dictionary to have a key of a file object?
If so, how do I initialise an empty file object? I mean, something
along the lines of:
fileAreaCode = open("", "r")
If not, any suggestions on achieving openning optional files in a loop?
Otherwise I'm stuck with:

---< BEGIN >---

# Optional input files
try:
fileAreaCode = open("areacode.11", "r")
except:
fileAreaCode = False

try:
fileBuild = open("build.11", "r")
except:
fileBuild = False

....

# Close files
for optionalFile in [fileAreaCode, fileBuild]:
if optionalFile:
print "Closing: %s" % str(optionalFile)
optionalFile.close()

---< END >---

Thanks,
Julian

 

[Brian Beck]

In this particular coding snippet, I was thinking of creating a
dictionary of file objects and file names. These would be optional
files that I could open and parse. At the end, I would easily close off
the files by iterating through the dictionary.

Hi,

File objects as keys sounds pretty dangerous. I'm curious why the first
thought that popped into your head wasn't using the file NAMES as keys
instead? Here's my go at it. (Is Google Groups nice to indentation using
spaces? I can't remember.)

optionalFiles = dict.fromkeys(['areacode.11', 'build.11'], None)

# To open optionalFiles...
for fileName in optionalFiles:
try:
optionalFiles[fileName] = open(fileName, "r")
print "Opened: %s" % fileName
except IOError:
# Values are already initialized to None.
print "File not found: %s" % fileName

# To close optionalFiles...
for fileName, fileObject in optionalFiles.iteritems():
if fileObject:
fileObject.close()
print "Closed: %s" % fileName
# Rebinding fileObject here won't modify the dictionary,
# so access it through the key.
optionalFiles[fileName] = None

 

[Julian Yap]

File objects as keys sounds pretty dangerous. I'm curious why the first
thought that popped into your head wasn't using the file NAMES as keys
instead? Here's my go at it. (Is Google Groups nice to indentation using
spaces? I can't remember.)

optionalFiles = dict.fromkeys(['areacode.11', 'build.11'], None)

# To open optionalFiles...
for fileName in optionalFiles:
try:
optionalFiles[fileName] = open(fileName, "r")
print "Opened: %s" % fileName
except IOError:
# Values are already initialized to None.
print "File not found: %s" % fileName

# To close optionalFiles...
for fileName, fileObject in optionalFiles.iteritems():
if fileObject:
fileObject.close()
print "Closed: %s" % fileName
# Rebinding fileObject here won't modify the dictionary,
# so access it through the key.
optionalFiles[fileName] = None

Brain,
Thanks for your help. I never thought of it like that.

I guess in my original thinking, in the processing of the optional files
I would start off each code block with something like:

if fileAreaCode:
...

But now I can just do:
if optionalFiles['areacode.11']:
...

I think I was just too much in the above mindset to think clearly about
the dictionary.

Using a file object as a key!? What was I thinking

Julian

 

[Brian Beck]

Call me a pedant, but what'd wrong with:

print 'closed: ' + filename
or
print 'closed:', filename

?

I always figure that debug-oriented output like that in example code is
very likely to be changed in format, or to include more information, by
the person actually using it. So string substitution makes it more
flexible; less work for them.

 

[jfj]

print "Closed: %s" % fileName

Call me a pedant, but what'd wrong with:

print 'closed: ' + filename
or
print 'closed:', filename

?

Modulus operator good but don't over-use it. Otherwise, bad style.


jfj