write data file

[SunX]

Question from a newbie. How do you write out a data file of floating
point numbers? file.write only takes strings.
Many thanks.

 

[Yermat]

Question from a newbie. How do you write out a data file of floating
point numbers? file.write only takes strings.
Many thanks.

Have a look at struct http://www.python.org/doc/2.3.3/lib/module-struct.html


Yermat

 

[Peter Otten]

Question from a newbie. How do you write out a data file of floating
point numbers? file.write only takes strings.
Many thanks.

The easiest way is to write them in a text file, one float per line.
You can use repr() or str() to convert them to a string:

somefloats = [1.2, 3.4, 5.7]
f = file("tmp.txt", "w")
for n in somefloats:

.... f.write(repr(n))
.... f.write("\n")
....

Here's how to read them back into Python:

f = file("tmp.txt")
readfloats = []
for line in f:

.... readfloats.append(float(line))
....[1.2, 3.3999999999999999, 5.7000000000000002]

The trailing digits are nothing to worry about (see the Python FAQ), for a
nicer appearance do

str(readfloats[1]) '3.4'
print readfloats[1] # uses str() for string conversion

3.4

When you are not interested in a human-readable file and have more complex
data to store, have a look at the pickle module.

Peter