257 lines
7 KiB
Python
257 lines
7 KiB
Python
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"""
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Page labels are shown by PDF viewers as "the page number".
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A page has a numeric index, starting with 0. Additionally to that, the page
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has a label. In the most simple case:
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label = index + 1
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However, the title page and the table of contents might have roman numerals as
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page label. This makes things more complicated.
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Example 1
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---------
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>>> reader.trailer["/Root"]["/PageLabels"]["/Nums"]
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[0, IndirectObject(18, 0, 139929798197504),
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8, IndirectObject(19, 0, 139929798197504)]
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>>> reader.get_object(reader.trailer["/Root"]["/PageLabels"]["/Nums"][1])
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{'/S': '/r'}
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>>> reader.get_object(reader.trailer["/Root"]["/PageLabels"]["/Nums"][3])
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{'/S': '/D'}
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Example 2
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---------
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The following example shows a document with pages labeled
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i, ii, iii, iv, 1, 2, 3, A-8, A-9, ...
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1 0 obj
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<< /Type /Catalog
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/PageLabels << /Nums [
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0 << /S /r >>
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4 << /S /D >>
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7 << /S /D
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/P ( A- )
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/St 8
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>>
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% A number tree containing
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% three page label dictionaries
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]
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>>
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...
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>>
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endobj
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PDF Specification 1.7
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=====================
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Table 159 – Entries in a page label dictionary
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----------------------------------------------
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The S-key:
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D Decimal arabic numerals
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R Uppercase roman numerals
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r Lowercase roman numerals
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A Uppercase letters (A to Z for the first 26 pages,
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AA to ZZ for the next 26, and so on)
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a Lowercase letters (a to z for the first 26 pages,
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aa to zz for the next 26, and so on)
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"""
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from typing import Iterator, Optional, Tuple
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from ._protocols import PdfReaderProtocol
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from ._utils import logger_warning
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from .generic import ArrayObject, DictionaryObject, NumberObject
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def number2uppercase_roman_numeral(num: int) -> str:
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roman = [
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(1000, "M"),
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(900, "CM"),
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(500, "D"),
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(400, "CD"),
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(100, "C"),
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(90, "XC"),
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(50, "L"),
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(40, "XL"),
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(10, "X"),
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(9, "IX"),
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(5, "V"),
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(4, "IV"),
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(1, "I"),
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]
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def roman_num(num: int) -> Iterator[str]:
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for decimal, roman_repr in roman:
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x, _ = divmod(num, decimal)
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yield roman_repr * x
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num -= decimal * x
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if num <= 0:
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break
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return "".join(list(roman_num(num)))
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def number2lowercase_roman_numeral(number: int) -> str:
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return number2uppercase_roman_numeral(number).lower()
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def number2uppercase_letter(number: int) -> str:
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if number <= 0:
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raise ValueError("Expecting a positive number")
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alphabet = [chr(i) for i in range(ord("A"), ord("Z") + 1)]
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rep = ""
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while number > 0:
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remainder = number % 26
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if remainder == 0:
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remainder = 26
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rep = alphabet[remainder - 1] + rep
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# update
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number -= remainder
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number = number // 26
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return rep
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def number2lowercase_letter(number: int) -> str:
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return number2uppercase_letter(number).lower()
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def index2label(reader: PdfReaderProtocol, index: int) -> str:
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"""
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See 7.9.7 "Number Trees".
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Args:
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reader: The PdfReader
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index: The index of the page
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Returns:
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The label of the page, e.g. "iv" or "4".
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"""
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root = reader.trailer["/Root"]
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if "/PageLabels" not in root:
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return str(index + 1) # Fallback
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number_tree = root["/PageLabels"]
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if "/Nums" in number_tree:
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# [Nums] shall be an array of the form
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# [ key 1 value 1 key 2 value 2 ... key n value n ]
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# where each key_i is an integer and the corresponding
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# value_i shall be the object associated with that key.
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# The keys shall be sorted in numerical order,
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# analogously to the arrangement of keys in a name tree
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# as described in 7.9.6, "Name Trees."
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nums = number_tree["/Nums"]
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i = 0
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value = None
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start_index = 0
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while i < len(nums):
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start_index = nums[i]
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value = nums[i + 1].get_object()
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if i + 2 == len(nums):
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break
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if nums[i + 2] > index:
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break
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i += 2
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m = {
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None: lambda n: "",
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"/D": lambda n: str(n),
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"/R": number2uppercase_roman_numeral,
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"/r": number2lowercase_roman_numeral,
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"/A": number2uppercase_letter,
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"/a": number2lowercase_letter,
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}
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# if /Nums array is not following the specification or if /Nums is empty
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if not isinstance(value, dict):
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return str(index + 1) # Fallback
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start = value.get("/St", 1)
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prefix = value.get("/P", "")
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return prefix + m[value.get("/S")](index - start_index + start)
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if "/Kids" in number_tree or "/Limits" in number_tree:
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logger_warning(
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(
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"/Kids or /Limits found in PageLabels. "
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"Please share this PDF with pypdf: "
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"https://github.com/py-pdf/pypdf/pull/1519"
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),
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__name__,
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)
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# TODO: Implement /Kids and /Limits for number tree
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return str(index + 1) # Fallback if /Nums is not in the number_tree
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def nums_insert(
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key: NumberObject,
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value: DictionaryObject,
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nums: ArrayObject,
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) -> None:
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"""
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Insert a key, value pair in a Nums array.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry
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value: value of the entry
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nums: Nums array to modify
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"""
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if len(nums) % 2 != 0:
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raise ValueError("a nums like array must have an even number of elements")
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i = len(nums)
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while i != 0 and key <= nums[i - 2]:
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i = i - 2
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if i < len(nums) and key == nums[i]:
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nums[i + 1] = value
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else:
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nums.insert(i, key)
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nums.insert(i + 1, value)
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def nums_clear_range(
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key: NumberObject,
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page_index_to: int,
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nums: ArrayObject,
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) -> None:
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"""
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Remove all entries in a number tree in a range after an entry.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry before the range
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page_index_to: The page index of the upper limit of the range
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nums: Nums array to modify
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"""
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if len(nums) % 2 != 0:
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raise ValueError("a nums like array must have an even number of elements")
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if page_index_to < key:
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raise ValueError("page_index_to must be greater or equal than key")
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i = nums.index(key) + 2
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while i < len(nums) and nums[i] <= page_index_to:
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nums.pop(i)
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nums.pop(i)
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def nums_next(
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key: NumberObject,
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nums: ArrayObject,
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) -> Tuple[Optional[NumberObject], Optional[DictionaryObject]]:
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"""
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Return the (key, value) pair of the entry after the given one.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry
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nums: Nums array
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"""
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if len(nums) % 2 != 0:
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raise ValueError("a nums like array must have an even number of elements")
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i = nums.index(key) + 2
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if i < len(nums):
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return (nums[i], nums[i + 1])
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else:
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return (None, None)
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