using data from a txt file in python

Question

I'm learning python and now I'm having some problems with reading and analyzing txt files. I want to open in python a .txt file that contains many lines and in each line I have one fruit and it's price.

I would like to know how to make python recognize their prices as a number (since it recognizes as a string when I use readlines()) so then I could use the numbers in some simple functions to calculate the minimum price that I have to sell the fruits to obtain profit.

Any ideas of how to do it?

Could you give some example lines fo your input file? Your format specification is quite vague. — Sven Marnach
– Sven Marnach, Commented Dec 14, 2011 at 16:41
It isn't. It's well understandable. There's a text file, on every line there are two space-separated values: a string and a number. He wants Python to read the second field as a number instead of a string. — user529758
– user529758, Commented Dec 14, 2011 at 16:42
@H2CO3: How do you know it's space-separated? aix interpreted it to be comma-spearated. And it also might be a CSV file exported from Excel, so we have to deal with quotes, or whatever. — Sven Marnach
– Sven Marnach, Commented Dec 14, 2011 at 16:46

NPE · Accepted Answer · 2011-12-14 16:42:36Z

1

If the name and the price are separated by a comma:

with open('data.txt') as f:
  for line in f:
    name, price = line.rstrip().split(',')
    price = float(price)
    print name, price

answered Dec 14, 2011 at 16:42

NPE

503k114 gold badges970 silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Zomgosh Over a year ago

well sorry I know I was quite vague but you really helped me a lot, Thank you =)

Shawn Chin · Accepted Answer · 2011-12-14 17:01:02Z

Assuming your values are space-separated, you can read in your file into a list of tuples using:

# generator to read file and return each line as a list of values
pairs = (line.split() for line in open("x.txt"))  
# use list comprehension to produce a list of tuples
fruits = [(name, float(price)) for name, price in pairs] 

print fruits
# will print [('apples', 1.23), ('pears', 231.23), ('guava', 12.3)]

Note that float() was used to convert the second value (price) from str to a floating point number.

See also: list comprehension and generator expression.

To make it easy to look up prices for each fruit, you can convert your list of tuples into a dict:

price_lookup = dict(fruits)

print price_lookup["apples"]
# will print 1.23

print price_lookup["guava"] * 2
# will print 24.6

See: dict().

Gordon Broom · Accepted Answer · 2011-12-14 16:53:21Z

0

I had the same problem when I first was learning Python, coming from Perl. Perl will "do what you mean" (or at least what it thinks you mean), and automatically convert something that looks like a number into a number when you try to use it like a number. (I'm generalizing, but you get the idea). The Python philosophy is to not have so much magic occurring, so you must do the conversion explicitly. Call either float("12.00") or int("123") to convert from strings.

answered Dec 14, 2011 at 16:53

Gordon Broom

3001 silver badge7 bronze badges

Collectives™ on Stack Overflow

using data from a txt file in python

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related