> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Valid Number Python Solution with Tests

> Tested Python solution for LeetCode 65 with 45 pytest cases. Generate a practice environment with lcpy.

LeetCode 65, [Hard](/catalog/hard). Topics: [String](/catalog/topics/string). [View on LeetCode](https://leetcode.com/problems/valid-number/description/).

Generate this problem as a practice environment: tested reference solution, 45 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 65   # by problem number
lcpy gen -s valid_number   # by problem name
```

## Problem

Given a string `s`, return whether `s` is a valid number.

For example, all the following are valid numbers: `"2"`, `"0089"`, `"-0.1"`, `"+3.14"`, `"4."`, `"-.9"`, `"2e10"`, `"-90E3"`, `"3e+7"`, `"+6e-1"`, `"53.5e93"`, `"-123.456e789"`, while the following are not valid numbers: `"abc"`, `"1a"`, `"1e"`, `"e3"`, `"99e2.5"`, `"--6"`, `"-+3"`, `"95a54e53"`.

Formally, a valid number is defined using one of the following definitions:

* An integer number followed by an optional exponent.
* A decimal number followed by an optional exponent.

An integer number is defined with an optional sign `'-'` or `'+'` followed by digits.

A decimal number is defined with an optional sign `'-'` or `'+'` followed by one of the following definitions:

* Digits followed by a dot `'.'`.
* Digits followed by a dot `'.'` followed by digits.
* A dot `'.'` followed by digits.

An exponent is defined with an exponent notation `'e'` or `'E'` followed by an integer number.

The digits are defined as one or more digits.

### Examples

```
Input: s = "0"
Output: true
```

```
Input: s = "e"
Output: false
```

```
Input: s = "."
Output: false
```

### Constraints

* 1 \<= s.length \<= 20
* s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/valid_number/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/valid_number/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(1)
    def is_number(self, s: str) -> bool:
        i, n = 0, len(s)

        def skip_digits() -> bool:
            nonlocal i
            start = i
            while i < n and s[i].isdigit():
                i += 1
            return i > start

        if s[i] in "+-":
            i += 1
        if skip_digits():
            if i < n and s[i] == ".":
                i += 1
                skip_digits()
        else:
            if i >= n or s[i] != ".":
                return False
            i += 1
            if not skip_digits():
                return False

        if i < n and s[i] in "eE":
            i += 1
            if i < n and s[i] in "+-":
                i += 1
            if not skip_digits():
                return False

        return i == n
```

## Complexity

| Time | Space |
| - | - |
| O(n) | O(1) |

## Tags


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