i want to convert a string into a float with Python 3.10.

The problem is the format of the string. For example:

"  3.841-11"

which stands for 3.841e-011.

I tried the classical

float("  3.841-11")

but this gives an error.

Just to change this one string is no solution, because i want to read a bigger file like this:

$$
$$  GRID Data
$$

GRID           1        -44.0332667.9   -2.55271
GRID           2        -39.1406667.9   -2.26907
GRID           3        -34.2481667.9   -1.98544
GRID           4        -29.3555667.9   -1.70181
GRID           5        -24.4629667.9   -1.41817
GRID           6        -19.5703667.9   -1.13454
GRID           7        -14.6777667.9   -.850903
GRID           8        -9.78516667.9   -.567269
GRID           9        -4.89258667.9   -.283634
GRID          10        3.055-13667.9   3.841-11
GRID          11        4.892579667.9   .2836343

This is my code:

    def read_fem(location):  
        mesh = open(location, 'r').read().splitlines()
    
        point = []
    
        for i in range(1, len(mesh)):
            if '$' not in mesh[i]:
    
                if 'GRID' in mesh[i]:
                    number = int(mesh[i][8:16])
                    x = float(mesh[i][24:32])
                    y = float(mesh[i][32:40])
                    z = float(mesh[i][40:48])
    
                    point.append([number, x, y, z])

Grateful for every answer.

CodePudding user response：

Replace - with e- before converting to float:

s = '3.841-11'

out = float(s.replace('-', 'e-'))

Output: 3.841e-11

A more generic approach if you can have e as well could be to use a regex:

import re

s = '3.841 4'

out = float(re.sub(r'(?=[- ])', 'e', s))

Output: 38410.0

CodePudding user response：

The following program will:

• assume the file is named: grid_data.txt
• look for hyphens surrounded by numbers eg. 3.841-11 and convert to 3.841e-11
• ignore hyphens at the beginning of numbers eg. -44.0332

The fix_float() function is allowing the conversion to happen.

• The regex in use is \d(-)\d

Code:

import re

pattern = re.compile(r'\d(-)\d')

def fix_float(m):
    val = m.group(0).replace('-','e-')
    return val

def read_fem(location):  
    mesh = open(location, 'r').read().splitlines()
    point = []

    for m in mesh:
        if '$' not in m:
            if 'GRID' in m:
                number = int(m[8:16])
                x = float(pattern.sub(fix_float, m[24:32]))
                y = float(pattern.sub(fix_float, m[32:40]))
                z = float(pattern.sub(fix_float, m[40:48]))

                point.append([number, x, y, z])
    return point


# Extract the data from the file                
data = read_fem('grid_data.txt')

# Display the data
for point in data:
    print(point)

Output:

[1, -44.0332, 667.9, -2.55271]
[2, -39.1406, 667.9, -2.26907]
[3, -34.2481, 667.9, -1.98544]
[4, -29.3555, 667.9, -1.70181]
[5, -24.4629, 667.9, -1.41817]
[6, -19.5703, 667.9, -1.13454]
[7, -14.6777, 667.9, -0.850903]
[8, -9.78516, 667.9, -0.567269]
[9, -4.89258, 667.9, -0.283634]
[10, 3.055e-13, 667.9, 3.841e-11]
[11, 4.892579, 667.9, 0.2836343]