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I am a newbie with Python and I search how to parse a .txt file. My .txt file is a namelist with computation informations like :

myfile.txt

var0 = 16
var1 = 1.12434E10
var2 = -1.923E-3
var3 = 920

How to read the values and put them in myvar0, myvar1, myvar2, myvar3 in python?

dlask
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Vincent
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  • Try python standard module [configparser](http://docs.python.org/library/configparser.html) – kev Feb 06 '12 at 14:19
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    NOTE: configparser throws a `MissingSectionHeaderError` if the file does not contain section headers and OP's example does not have headers. The custom solution by @Lauritz is probably simpler than [possible workarounds for using configparser with no headers](http://stackoverflow.com/questions/22501121/configparser-missingsectionheadererror-when-parsing-rsyncd-config-file-with-glob). – 7yl4r Mar 13 '17 at 18:48

7 Answers7

71

I suggest storing the values in a dictionary instead of in separate local variables:

myvars = {}
with open("namelist.txt") as myfile:
    for line in myfile:
        name, var = line.partition("=")[::2]
        myvars[name.strip()] = float(var)

Now access them as myvars["var1"]. If the names are all valid python variable names, you can put this below:

names = type("Names", [object], myvars)

and access the values as e.g. names.var1.

Lauritz V. Thaulow
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  • In my case he use of strip() on name was redundant, but the newline on var caused a problem. So what worked better for me was myvars[name] = float(var.strip()) – snow6oy Jan 07 '16 at 18:24
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    what happens if the file cas comments '# this is a comment line' – Aryeh Armon Nov 09 '16 at 08:21
  • @snow6oy `float(val)` and `float(val.strip())` are equivalent – Francesco Frassinelli Oct 09 '18 at 10:40
  • If you have comments '# this is a comment line' in your file, just check the empty condition in you var variable and assign. for example, add the below if condition before assigning. this would ignore the commented line, if var: myvars[name.strip()] = float(var) Note: ensure you don't have any "=" symbol in your commented line – Daniel Inbaraj Mar 21 '22 at 09:40
10

I personally solved this by creating a .py file that just contains all the parameters as variables - then did:

include PARAMETERS.py

in the program modules that need the parameters.

It's a bit ugly, but VERY simple and easy to work with.

John Bailey
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7

Dict comprehensions (PEP 274) can be used for a shorter expression (60 characters):

d = {k:float(v) for k, v in (l.split('=') for l in open(f))}

EDIT: shortened from 72 to 60 characters thanks to @jmb suggestion (avoid .readlines()).

Francesco Frassinelli
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3

As @kev suggests, the configparser module is the way to go.

However in some scenarios (a bit ugly, I admit) but very simple and effective way to do to this is to rename myfile.txt to myfile.py and do a from myfile import * (after you fix the typo var 0 -> var0)

However, this is very insecure, so if the file is from an external source or can be written by a malicious attacker, use something that validates the data instead of executing it blindly.

Kimvais
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0

If there are multiple comma-separated values on a single line, here's code to parse that out:

    res = {}                                                                                                                                                                                             

    pairs = args.split(", ")                                                                                                                                                                             
    for p in pairs:                                                                                                                                                                                      
        var, val = p.split("=")                                                                                                                                                                          
        res[var] = val
Lana Nova
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0

Use pandas.read_csv when the file format becomes more fancy (like comments). 

val = u'''var0 = 16
var1 = 1.12434E10
var2 = -1.923E-3
var3 = 920'''
print(pandas.read_csv(StringIO(val), # or read_csv('myfile.txt',
            delimiter='\s*=\s*',
            header=None,
            names=['key','value'],
            dtype=dict(key=numpy.object,value=numpy.object), # or numpy.float64
            index_col=['key']).to_dict()['value'])
# prints {u'var1': u'1.12434E10', u'var0': u'16', u'var3': u'920', u'var2': u'-1.923E-3'}
rwitzel
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0

Similar to @lauritz-v-thaulow but, just a line by line read into a variable.

Here is a simple Copy-Pasta so you can understand a bit more.
As the config file has to be a specific format.

import os

# Example creating an valid temp test file to get a better result. 
MY_CONFIG = os.path.expanduser('~/.test_credentials')
with open(MY_CONFIG, "w") as f:
    f.write("API_SECRET_KEY=123456789")
    f.write(os.linesep)
    f.write("API_SECRET_CONTENT=12345678")

myvars = {}
with open(MY_CONFIG, "r") as myfile:
    for line in myfile:
        line = line.strip()
        name, var = line.partition("=")[::2]
        myvars[name.strip()] = str(var)

# Iterate thru all the items created.
for k, v in myvars.items():
    print("{} | {}".format(k, v))

# API_SECRET_KEY | 123456789
# API_SECRET_CONTENT | 12345678

# Access the API_SECRET_KEY item directly
print("{}".format(myvars['API_SECRET_KEY']))

# 123456789

# Access the API_SECRET_CONTENT item directly
print("{}".format(myvars['API_SECRET_CONTENT']))

# 12345678
JayRizzo
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