[Tutor] Reading Input Data

[Kent Johnson]

Michael Langford wrote:
> for subscript,line in enumerate(file("file.csv")):
>      s = line.split(",")[1]
>      try:
> 	     f = float(s)
> 	     locals()["x%i" % subscript]=f
>      except:
> 	     locals()["x%i" % subscript]=s

Don't do this!

For one thing, writing to locals() doesn't always work. Specifically, 
writing to locals() inside a function does *not* affect the local namespace:
In [28]: def foo():
    ....:     locals()['x'] = 1
    ....:     print x
    ....:
    ....:
In [29]: foo()
------------------------------------------------------------
Traceback (most recent call last):
   File "<ipython console>", line 1, in <module>
   File "<ipython console>", line 3, in foo
<type 'exceptions.NameError'>: global name 'x' is not defined


Writing to globals() might be marginally better but not much. (When not 
in a function, locals() is actually the same as globals() and the above 
code will work.)

In most cases where someone is trying to assign a bunch of names like 
this, a better solution is to use a dictionary (or possibly a list) to 
hold the data.

Kent