DOC: Migration guide (PyPDF2 1.x ➔ 2.x)

docs/index.rst

@@ -19,6 +19,7 @@ You can contribute to `PyPDF2 on Github <https://github.com/py-pdf/PyPDF2>`_.
    :maxdepth: 1
 
    user/installation
+   user/migration-1-to-2
    user/robustness
    user/suppress-warnings
    user/metadata

docs/user/migration-1-to-2.md

@@ -0,0 +1,75 @@
+# Migration Guide: 1.x to 2.x
+
+`PyPDF2<2.0.0` ([docs](https://pypdf2.readthedocs.io/en/1.27.12/meta/history.html))
+is very different from `PyPDF2>=2.0.0` ([docs](https://pypdf2.readthedocs.io/en/latest/meta/history.html)).
+
+Luckily, most changes are simple naming adjustments. This guide helps you to
+make the step from `PyPDF2 1.x` (or even the original PyPpdf) to `PyPDF2>=2.0.0`.
+
+You can execute your code with the updated version and show deprecation warnings
+by running `python -W all your_code.py`.
+
+# Imports and Modules
+
+* `PyPDF2.utils` no longer exists
+* `PyPDF2.pdf` no longer exists. You can import from `PyPDF2` directly or from
+  `PyPDF2.generic`
+
+# Naming Adjustments
+
+## Classes
+
+The base classes were renamed as they also allow to operate with ByteIO streams
+instead of files. Also, the `strict` paramter changed the default value from
+`strict=True` to `strict=False`.
+
+* `PdfFileReader` ➔ `PdfReader`
+* `PdfFileWriter` ➔ `PdfWriter`
+* `PdfFileMerger` ➔ `PdfMerger`
+
+PdfFileReader and PdfFileMerger no longer have the `overwriteWarnings`
+parameter. The new behavior is `overwriteWarnings=False`.
+
+## Function, Method, and Property Names
+
+In `PyPDF2.xmp.XmpInformation`:
+
+* `rdfRoot` ➔ `rdf_root`
+* `xmp_createDate` ➔ `xmp_create_date`
+* `xmp_creatorTool` ➔ `xmp_creator_tool`
+* `xmp_metadataDate` ➔ `xmp_metadata_date`
+* `xmp_modifyDate` ➔ `xmp_modify_date`
+* `xmpMetadata` ➔ `xmp_metadata`
+* `xmpmm_documentId` ➔ `xmpmm_document_id`
+* `xmpmm_instanceId` ➔ `xmpmm_instance_id`
+
+In `PyPDF2.generic`:
+
+* `readHexStringFromStream` ➔ `read_hex_string_from_stream`
+* `initializeFromDictionary` ➔ `initialize_from_dictionary`
+* `createStringObject` ➔ `create_string_object`
+* `TreeObject.hasChildren` ➔ `TreeObject.has_children`
+* `TreeObject.emptyTree` ➔ `TreeObject.empty_tree`
+
+## Parameter Names
+
+* `PdfWriter.get_page`: `pageNumber` ➔ `page_number`
+* `PyPDF2.filters` (all classes): `decodeParms` ➔ `decode_parms`
+* `PyPDF2.filters` (all classes): `decodeStreamData` ➔ `decode_stream_data`
+
+## Deprecations
+
+A few classes / functions were deprecated without replacement:
+
+* `PyPDF2.utils.ConvertFunctionsToVirtualList`
+* `PyPDF2.utils.formatWarning`
+* `PyPDF2.isInt(obj)`: Use `instance(obj, int)` instead
+* `PyPDF2.u_(s)`: Use `s` directly
+* `PyPDF2.chr_(c)`: Use `chr(c)` instead
+* `PyPDF2.barray(b)`: Use `bytearray(b)` instead
+* `PyPDF2.isBytes(b)`: Use `instance(b, type(bytes()))` instead
+* `PyPDF2.xrange_fn`: Use `range` instead
+* `PyPDF2.string_type`: Use `str` instead
+* `PyPDF2.isString(s)`: Use `instance(s, str)` instead
+* `PyPDF2._basestring`: Use `str` instead
+* `b_(...)` was removed. You should typically be able use the bytes object directly, otherwise you can [copy this](https://github.com/py-pdf/PyPDF2/pull/986#issuecomment-1230698069)