Python order of execution

Question

I was wondering if Python has similar issues as C regarding the order of execution of certain elements of code.

For example, I know in C there are times say when it's not guaranteed that some variable is initialized before another. Or just because one line of code is above another it's not guaranteed that it is implemented before all the ones below it.

Is it the same for Python? Like if I open a file of data, read in the data, close the file, then do other stuff do I know for sure that the file is closed before the lines after I close the file are executed??

The reason I ask is because I'm trying to read in a large file of data (1.6GB) and use this python module specific to the work I do on the data. When I run this module I get this error message:

    File "/glast01/software/ScienceTools/ScienceTools-v9r15p2-SL4/sane/v3r18p1/python/GtApp.py", line 57, in run
    input, output = self.runWithOutput(print_command)
  File "/glast01/software/ScienceTools/ScienceTools-v9r15p2-SL4/sane/v3r18p1/python/GtApp.py", line 77, in runWithOutput
    return os.popen4(self.command(print_command))
  File "/Home/eud/jmcohen/.local/lib/python2.5/os.py", line 690, in popen4
    stdout, stdin = popen2.popen4(cmd, bufsize)
  File "/Home/eud/jmcohen/.local/lib/python2.5/popen2.py", line 199, in popen4
    inst = Popen4(cmd, bufsize)
  File "/Home/eud/jmcohen/.local/lib/python2.5/popen2.py", line 125, in __init__
    self.pid = os.fork()
OSError: [Errno 12] Cannot allocate memory
>>> 
Exception exceptions.AttributeError: AttributeError("Popen4 instance has no attribute 'pid'",) in <bound method Popen4.__del__ of <popen2.Popen4 instance at 0x9ee6fac>> ignored

I assume it's related to the size of the data I read in (it has 17608310 rows and 22 columns). I thought perhaps if I closed the file I opened right after I read in the data this would help, but it didn't. This led me to thinking about the order that lines of code are executed in, hence my question.

Thanks

Answer 1

The only thing I can think of that may surprise some people is:

def test():
    try:
        return True
    finally:
        return False

print test()

Output:

False

finally clauses really are executed last, even if a return statement precedes them. However, this is not specific to Python.

Answer 2

Execution of C certainly is sequential, for actual statements. There are even rules that define the sequence points, so you can know how individual expressions evaluate.