How to Use Regular Expressions to Extract Float/Double Values in Python?

Extracting Float/Double Values with Regular Expressions

In Python, you can utilize regular expressions to extract floating-point or double values from strings. Let's explore a powerful regular expression from Perl:

(?x)
^
  [+-]?\ *      # Optional sign followed by optional whitespace
  (             # Match integers or floating-point mantissas
      \d+       # Whole numbers
      (
          \.\d* # Mantissa with decimal point (a.b or a.)
      )?        # Optional decimal point
     |\.\d+     # Mantissa without leading whole number (.b)
  )
  ([eE][+-]?\d+)?  # Optional exponent
$

For example, to extract a double value from a string:

<code class="python">import re

# Create a regular expression pattern
re_float = re.compile(above_regexp)

# Match the pattern against a string
match = re_float.match("4.5")

# Extract the matched value
double_value = match.group(0)

print(double_value)  # Output: 4.5</code>

To extract multiple numeric values from a larger string, you can use the findall() method:

<code class="python">s = """4.5 abc -4.5 abc - 4.5 abc + .1e10 abc . abc 1.01e-2 abc 
       1.01e-.2 abc 123 abc .123"""

numeric_values = re.findall(r"[+-]? *(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?", s)

print(numeric_values)  # Output: ['4.5', '-4.5', '- 4.5', '+ .1e10', ' 1.01e-2', '       1.01', '-.2', ' 123', ' .123']</code>

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