# XPath Quick Reference

*Axes, predicates, functions, operators, node selection*

> Source: XPath Specification (w3.org/TR/xpath) · MIT

## Syntax

### Path Expressions

| Command | Description |
|---------|-------------|
| `/` | Root node (absolute path start) |
| `/bookstore/book` | Direct child selection |
| `//book` | Select all book nodes anywhere |
| `.` | Current context node |
| `..` | Parent of current node |
| `@lang` | Attribute named lang |
| `node()` | Any node of any type |
| `*` | Any element node |
| `@*` | Any attribute |

### Basic Examples

```
/html/body/div          # absolute path to <div>
//input[@type='text']   # all text inputs
//div[@class='main']/*  # children of div.main
//a/@href               # all href attributes
```

### Combining Paths

```
//book/title | //book/price   # union of two paths
//h1 | //h2 | //h3           # multiple element types
```

## Axes

### Axis Directions

| Command | Description |
|---------|-------------|
| `child::` | Direct children (default axis) |
| `parent::` | Direct parent |
| `ancestor::` | All ancestors to root |
| `ancestor-or-self::` | Ancestors + current node |
| `descendant::` | All descendants |
| `descendant-or-self::` | Descendants + current node |
| `following::` | All nodes after current in document |
| `following-sibling::` | Siblings after current |
| `preceding::` | All nodes before current in document |
| `preceding-sibling::` | Siblings before current |
| `self::` | Current node only |
| `attribute::` | Attributes of current node |
| `namespace::` | Namespace nodes |

### Axis Examples

```
//div/child::p             # <p> children of <div>
//td/parent::tr            # <tr> parent of <td>
//h2/following-sibling::p  # <p> after <h2>
//li/ancestor::ul          # <ul> containing <li>
```

## Predicates

### Filtering with Predicates

```
//book[1]                  # first book element
//book[last()]             # last book element
//book[position() < 3]    # first two books
//book[@lang='en']        # books with lang="en"
//book[price > 30]        # books with price > 30
```

### Predicate Patterns

| Command | Description |
|---------|-------------|
| `[n]` | Element at position n (1-based) |
| `[last()]` | Last element |
| `[last()-1]` | Second to last |
| `[@attr]` | Has attribute |
| `[@attr='val']` | Attribute equals value |
| `[element]` | Has child element |
| `[element='text']` | Child element contains text |
| `[not(@attr)]` | Does not have attribute |

### Chained Predicates

```
//div[@class='list']//a[1]         # first <a> in div.list
//input[@type='text'][@name='q']   # AND condition
//book[price>30][@lang='en']       # multiple conditions
```

## Functions

### String Functions

| Command | Description |
|---------|-------------|
| `contains(s, sub)` | True if s contains sub |
| `starts-with(s, pre)` | True if s starts with pre |
| `string-length(s)` | Length of string |
| `normalize-space(s)` | Trim and collapse whitespace |
| `concat(a, b, ...)` | Join strings |
| `substring(s, pos, len)` | Extract substring (1-based) |
| `translate(s, from, to)` | Character-by-character replace |

### Numeric Functions

| Command | Description |
|---------|-------------|
| `sum(node-set)` | Sum of numeric values |
| `count(node-set)` | Number of nodes |
| `floor(n)` | Round down |
| `ceiling(n)` | Round up |
| `round(n)` | Round to nearest integer |
| `number(val)` | Convert to number |

### Function Examples

```
//div[contains(@class, 'active')]
//a[starts-with(@href, 'https')]
//p[string-length(text()) > 100]
//ul[count(li) > 5]
```

## Operators

### Comparison Operators

| Command | Description |
|---------|-------------|
| `=` | Equal |
| `!=` | Not equal |
| `<` | Less than |
| `<=` | Less than or equal |
| `>` | Greater than |
| `>=` | Greater than or equal |

### Logical & Arithmetic

| Command | Description |
|---------|-------------|
| `and` | Logical AND |
| `or` | Logical OR |
| `not()` | Logical NOT (function) |
| `+` | Addition |
| `-` | Subtraction |
| `*` | Multiplication |
| `div` | Division |
| `mod` | Modulus |
| `\|` | Union of node sets |

### Operator Examples

```
//book[price > 20 and price < 50]
//item[@type='a' or @type='b']
//span[not(contains(@class, 'hidden'))]
```

## Node Tests

### Node Types

| Command | Description |
|---------|-------------|
| `node()` | Any node (element, text, comment, PI) |
| `text()` | Text node only |
| `comment()` | Comment node only |
| `processing-instruction()` | Processing instruction node |
| `*` | Any element node |
| `@*` | Any attribute node |
| `element-name` | Element with specific name |

### Node Test Examples

```
//p/text()                # text content of <p>
//div/comment()           # comments inside <div>
//body/node()             # all child nodes of <body>
//div/*                   # all element children of <div>
```

### Boolean Functions

| Command | Description |
|---------|-------------|
| `true()` | Boolean true |
| `false()` | Boolean false |
| `boolean(expr)` | Convert to boolean |
| `not(expr)` | Negate boolean |
| `lang(code)` | True if node's lang matches |

## Abbreviations

### Short vs Long Form

| Command | Description |
|---------|-------------|
| `(none)` | child:: (default axis) |
| `@` | attribute:: |
| `//` | /descendant-or-self::node()/ |
| `.` | self::node() |
| `..` | parent::node() |
| `[n]` | [position()=n] |

### Abbreviated Examples

```
# These pairs are equivalent:
child::div            →  div
attribute::href       →  @href
/descendant-or-self::node()/p  →  //p
self::node()          →  .
parent::node()        →  ..
```

### Common Abbreviated Patterns

```
//div[@id='main']       # div with id="main"
//table//td             # all <td> in any <table>
../sibling              # sibling via parent
.//span                 # span descendants of context
```

## Common Patterns

### Web Scraping / Testing

```
//input[@name='username']          # form input by name
//button[text()='Submit']          # button by text
//div[contains(@class, 'error')]   # element by partial class
//a[contains(@href, 'login')]      # link by partial href
```

### Conditional Selection

```
//div[@class='item'][.//span[@class='price']]
//tr[td[1]='Active']              # row where 1st cell = Active
//*[contains(text(), 'Warning')]   # any element with text
```

### XPath in Python (lxml)

```
from lxml import html
tree = html.fromstring(page_content)
links = tree.xpath('//a/@href')
titles = tree.xpath('//h2/text()')
```

### XPath in Selenium

```
driver.find_element(By.XPATH, "//input[@id='search']")
driver.find_elements(By.XPATH, "//li[@class='result']")
```