You want to match a floating-point number and specify whether the sign, integer, fraction and exponent parts of the number are required, optional, or disallowed. You don’t want to use the regular expression to restrict the numbers to a specific range, and instead leave that to procedural code, as explained in Recipe 3.12.

Mandatory sign, integer, fraction, and exponent:

^[-+][0-9]+\.[0-9]+[eE][-+]?[0-9]+$

Regex options:
None |

Regex flavors: .NET,
Java, JavaScript, PCRE, Perl, Python, Ruby |

Mandatory sign, integer, and fraction, but no exponent:

^[-+][0-9]+\.[0-9]+$

Regex options:
None |

Regex flavors: .NET,
Java, JavaScript, PCRE, Perl, Python, Ruby |

Optional sign, mandatory integer and fraction, and no exponent:

^[-+]?[0-9]+\.[0-9]+$

Regex options:
None |

Regex flavors: .NET,
Java, JavaScript, PCRE, Perl, Python, Ruby |

Optional sign and integer, mandatory fraction, and no exponent:

^[-+]?[0-9]*\.[0-9]+$

Regex options:
None |

Regex flavors: .NET,
Java, JavaScript, PCRE, Perl, Python, Ruby |

Optional sign, integer, and fraction. If the integer part is omitted, the fraction is mandatory. If the fraction is omitted, the decimal dot must be omitted, too. No exponent.

^[-+]?([0-9]+(\.[0-9]+)?|\.[0-9]+)$

Regex options:
None |

Regex flavors: .NET,
Java, JavaScript, PCRE, Perl, Python, Ruby |

Optional sign, integer, and fraction. If the integer part is omitted, the fraction is mandatory. If the fraction is omitted, the decimal dot is optional. No exponent.

^[-+]?([0-9]+(\.[0-9]*)?|\.[0-9]+)$ ...

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