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  21 <header>
  22 <h1 class="title">Module <code>szyfrow.railfence</code></h1>
  23 </header>
  24 <section id="section-intro">
  25 <p><a href="https://en.wikipedia.org/wiki/Rail_fence_cipher">Railfence transposition cipher</a>.</p>
  26 <p>Works by splitting the text into sections, then reading across them to
  27 generate the rows in the cipher. The rows are then combined to form the
  28 ciphertext.</p>
  29 <p>Example: the plaintext "hellotherefriends", with a height of four, written
  30 out in the railfence as
  31 h h i
  32 etere*
  33 lorfns
  34 l e d
  35 (with the * showing the one character to finish the last section).
  36 Each 'section' is two columns, but unfolded. In the example, the first
  37 section is 'hellot'.</p>
  38 <details class="source">
  39 <summary>
  40 <span>Expand source code</span>
  41 </summary>
  42 <pre><code class="python">&#34;&#34;&#34;[Railfence transposition cipher](https://en.wikipedia.org/wiki/Rail_fence_cipher).
  43
  44 Works by splitting the text into sections, then reading across them to
  45 generate the rows in the cipher. The rows are then combined to form the
  46 ciphertext.
  47
  48 Example: the plaintext &#34;hellotherefriends&#34;, with a height of four, written
  49 out in the railfence as
  50    h h i
  51    etere*
  52    lorfns
  53    l e d
  54 (with the * showing the one character to finish the last section).
  55 Each &#39;section&#39; is two columns, but unfolded. In the example, the first
  56 section is &#39;hellot&#39;.
  57 &#34;&#34;&#34;
  58 import math
  59 from enum import Enum
  60 from itertools import starmap, zip_longest
  61 from szyfrow.support.utilities import *
  62 from szyfrow.support.language_models import *
  63
  64
  65 def railfence_encipher(message, height, fillvalue=&#39;&#39;):
  66     &#34;&#34;&#34;Railfence cipher.
  67     Works by splitting the text into sections, then reading across them to
  68     generate the rows in the cipher. The rows are then combined to form the
  69     ciphertext.
  70
  71     Example: the plaintext &#34;hellotherefriends&#34;, with a height of four, written
  72     out in the railfence as
  73        h h i
  74        etere*
  75        lorfns
  76        l e d
  77     (with the * showing the one character to finish the last section).
  78     Each &#39;section&#39; is two columns, but unfolded. In the example, the first
  79     section is &#39;hellot&#39;.
  80
  81     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 2, fillvalue=&#39;!&#39;)
  82     &#39;hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!&#39;
  83     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 3, fillvalue=&#39;!&#39;)
  84     &#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!&#39;
  85     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 5, fillvalue=&#39;!&#39;)
  86     &#39;hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!&#39;
  87     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 10, fillvalue=&#39;!&#39;)
  88     &#39;hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!&#39;
  89     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 3)
  90     &#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece&#39;
  91     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 5)
  92     &#39;hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp&#39;
  93     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 7)
  94     &#39;haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic&#39;
  95     &#34;&#34;&#34;
  96     sections = chunks(message, (height - 1) * 2, fillvalue=fillvalue)
  97     n_sections = len(sections)
  98     # Add the top row
  99     rows = [cat([s[0] for s in sections])]
 100     # process the middle rows of the grid
 101     for r in range(1, height-1):
 102         rows += [cat([s[r:r+1] + s[height*2-r-2:height*2-r-1] for s in sections])]
 103     # process the bottom row
 104     rows += [cat([s[height - 1:height] for s in sections])]
 105     # rows += [wcat([s[height - 1] for s in sections])]
 106     return cat(rows)
 107
 108 def railfence_decipher(message, height, fillvalue=&#39;&#39;):
 109     &#34;&#34;&#34;Railfence decipher.
 110     Works by reconstructing the grid used to generate the ciphertext, then
 111     unfolding the sections so the text can be concatenated together.
 112
 113     Example: given the ciphertext &#39;hhieterelorfnsled&#39; and a height of 4, first
 114     work out that the second row has a character missing, find the rows of the
 115     grid, then split the section into its two columns.
 116
 117     &#39;hhieterelorfnsled&#39; is split into
 118         h h i
 119         etere
 120         lorfns
 121         l e d
 122     (spaces added for clarity), which is stored in &#39;rows&#39;. This is then split
 123     into &#39;down_rows&#39; and &#39;up_rows&#39;:
 124
 125     down_rows:
 126        hhi
 127        eee
 128        lrn
 129        led
 130
 131     up_rows:
 132        tr
 133        ofs
 134
 135     These are then zipped together (after the up_rows are reversed) to recover
 136     the plaintext.
 137
 138     Most of the procedure is about finding the correct lengths for each row then
 139     splitting the ciphertext into those rows.
 140
 141     &gt;&gt;&gt; railfence_decipher(&#39;hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!&#39;, 2).strip(&#39;!&#39;)
 142     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 143     &gt;&gt;&gt; railfence_decipher(&#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!&#39;, 3).strip(&#39;!&#39;)
 144     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 145     &gt;&gt;&gt; railfence_decipher(&#39;hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!&#39;, 5).strip(&#39;!&#39;)
 146     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 147     &gt;&gt;&gt; railfence_decipher(&#39;hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!&#39;, 10).strip(&#39;!&#39;)
 148     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 149     &gt;&gt;&gt; railfence_decipher(&#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece&#39;, 3)
 150     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 151     &gt;&gt;&gt; railfence_decipher(&#39;hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp&#39;, 5)
 152     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 153     &gt;&gt;&gt; railfence_decipher(&#39;haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic&#39;, 7)
 154     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 155     &#34;&#34;&#34;
 156     # find the number and size of the sections, including how many characters
 157     #   are missing for a full grid
 158     n_sections = math.ceil(len(message) / ((height - 1) * 2))
 159     padding_to_add = n_sections * (height - 1) * 2 - len(message)
 160     # row_lengths are for the both up rows and down rows
 161     row_lengths = [n_sections] * (height - 1) * 2
 162     for i in range((height - 1) * 2 - 1, (height - 1) * 2 - (padding_to_add + 1), -1):
 163         row_lengths[i] -= 1
 164     # folded_rows are the combined row lengths in the middle of the railfence
 165     folded_row_lengths = [row_lengths[0]]
 166     for i in range(1, height-1):
 167         folded_row_lengths += [row_lengths[i] + row_lengths[-i]]
 168     folded_row_lengths += [row_lengths[height - 1]]
 169     # find the rows that form the railfence grid
 170     rows = []
 171     row_start = 0
 172     for i in folded_row_lengths:
 173         rows += [message[row_start:row_start + i]]
 174         row_start += i
 175     # split the rows into the &#39;down_rows&#39; (those that form the first column of
 176     #   a section) and the &#39;up_rows&#39; (those that ofrm the second column of a
 177     #   section).
 178     down_rows = [rows[0]]
 179     up_rows = []
 180     for i in range(1, height-1):
 181         down_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 0])]
 182         up_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 1])]
 183     down_rows += [rows[-1]]
 184     up_rows.reverse()
 185     return cat(c for r in zip_longest(*(down_rows + up_rows), fillvalue=&#39;&#39;) for c in r)
 186
 187
 188 def railfence_break(message, max_key_length=20,
 189                      fitness=Pbigrams, chunksize=500):
 190     &#34;&#34;&#34;Breaks a railfence cipher using a range of lengths and
 191     n-gram frequency analysis
 192
 193     &gt;&gt;&gt; railfence_break(railfence_encipher(sanitise( \
 194             &#34;It is a truth universally acknowledged, that a single man in \
 195              possession of a good fortune, must be in want of a wife. However \
 196              little known the feelings or views of such a man may be on his \
 197              first entering a neighbourhood, this truth is so well fixed in \
 198              the minds of the surrounding families, that he is considered the \
 199              rightful property of some one or other of their daughters.&#34;), \
 200         7)) # doctest: +ELLIPSIS
 201     (7, -709.46467226...)
 202     &gt;&gt;&gt; railfence_break(railfence_encipher(sanitise( \
 203             &#34;It is a truth universally acknowledged, that a single man in \
 204              possession of a good fortune, must be in want of a wife. However \
 205              little known the feelings or views of such a man may be on his \
 206              first entering a neighbourhood, this truth is so well fixed in \
 207              the minds of the surrounding families, that he is considered the \
 208              rightful property of some one or other of their daughters.&#34;), \
 209         7), \
 210         fitness=Ptrigrams) # doctest: +ELLIPSIS
 211     (7, -997.0129085...)
 212     &#34;&#34;&#34;
 213     def worker(message, height, fitness):
 214         plaintext = railfence_decipher(message, height)
 215         fit = fitness(plaintext)
 216         return height, fit
 217
 218     sanitised_message = sanitise(message)
 219     results = starmap(worker, [(sanitised_message, i, fitness)
 220                                for i in range(2, max_key_length+1)])
 221     return max(results, key=lambda k: k[1])</code></pre>
 222 </details>
 223 </section>
 224 <section>
 225 </section>
 226 <section>
 227 </section>
 228 <section>
 229 <h2 class="section-title" id="header-functions">Functions</h2>
 230 <dl>
 231 <dt id="szyfrow.railfence.cat"><code class="name flex">
 232 <span>def <span class="ident">cat</span></span>(<span>iterable, /)</span>
 233 </code></dt>
 234 <dd>
 235 <div class="desc"><p>Concatenate any number of strings.</p>
 236 <p>The string whose method is called is inserted in between each given string.
 237 The result is returned as a new string.</p>
 238 <p>Example: '.'.join(['ab', 'pq', 'rs']) -&gt; 'ab.pq.rs'</p></div>
 239 </dd>
 240 <dt id="szyfrow.railfence.lcat"><code class="name flex">
 241 <span>def <span class="ident">lcat</span></span>(<span>iterable, /)</span>
 242 </code></dt>
 243 <dd>
 244 <div class="desc"><p>Concatenate any number of strings.</p>
 245 <p>The string whose method is called is inserted in between each given string.
 246 The result is returned as a new string.</p>
 247 <p>Example: '.'.join(['ab', 'pq', 'rs']) -&gt; 'ab.pq.rs'</p></div>
 248 </dd>
 249 <dt id="szyfrow.railfence.railfence_break"><code class="name flex">
 250 <span>def <span class="ident">railfence_break</span></span>(<span>message, max_key_length=20, fitness=&lt;function Pbigrams&gt;, chunksize=500)</span>
 251 </code></dt>
 252 <dd>
 253 <div class="desc"><p>Breaks a railfence cipher using a range of lengths and
 254 n-gram frequency analysis</p>
 255 <pre><code class="language-python-repl">&gt;&gt;&gt; railfence_break(railfence_encipher(sanitise(             &quot;It is a truth universally acknowledged, that a single man in              possession of a good fortune, must be in want of a wife. However              little known the feelings or views of such a man may be on his              first entering a neighbourhood, this truth is so well fixed in              the minds of the surrounding families, that he is considered the              rightful property of some one or other of their daughters.&quot;),         7)) # doctest: +ELLIPSIS
 256 (7, -709.46467226...)
 257 &gt;&gt;&gt; railfence_break(railfence_encipher(sanitise(             &quot;It is a truth universally acknowledged, that a single man in              possession of a good fortune, must be in want of a wife. However              little known the feelings or views of such a man may be on his              first entering a neighbourhood, this truth is so well fixed in              the minds of the surrounding families, that he is considered the              rightful property of some one or other of their daughters.&quot;),         7),         fitness=Ptrigrams) # doctest: +ELLIPSIS
 258 (7, -997.0129085...)
 259 </code></pre></div>
 260 <details class="source">
 261 <summary>
 262 <span>Expand source code</span>
 263 </summary>
 264 <pre><code class="python">def railfence_break(message, max_key_length=20,
 265                      fitness=Pbigrams, chunksize=500):
 266     &#34;&#34;&#34;Breaks a railfence cipher using a range of lengths and
 267     n-gram frequency analysis
 268
 269     &gt;&gt;&gt; railfence_break(railfence_encipher(sanitise( \
 270             &#34;It is a truth universally acknowledged, that a single man in \
 271              possession of a good fortune, must be in want of a wife. However \
 272              little known the feelings or views of such a man may be on his \
 273              first entering a neighbourhood, this truth is so well fixed in \
 274              the minds of the surrounding families, that he is considered the \
 275              rightful property of some one or other of their daughters.&#34;), \
 276         7)) # doctest: +ELLIPSIS
 277     (7, -709.46467226...)
 278     &gt;&gt;&gt; railfence_break(railfence_encipher(sanitise( \
 279             &#34;It is a truth universally acknowledged, that a single man in \
 280              possession of a good fortune, must be in want of a wife. However \
 281              little known the feelings or views of such a man may be on his \
 282              first entering a neighbourhood, this truth is so well fixed in \
 283              the minds of the surrounding families, that he is considered the \
 284              rightful property of some one or other of their daughters.&#34;), \
 285         7), \
 286         fitness=Ptrigrams) # doctest: +ELLIPSIS
 287     (7, -997.0129085...)
 288     &#34;&#34;&#34;
 289     def worker(message, height, fitness):
 290         plaintext = railfence_decipher(message, height)
 291         fit = fitness(plaintext)
 292         return height, fit
 293
 294     sanitised_message = sanitise(message)
 295     results = starmap(worker, [(sanitised_message, i, fitness)
 296                                for i in range(2, max_key_length+1)])
 297     return max(results, key=lambda k: k[1])</code></pre>
 298 </details>
 299 </dd>
 300 <dt id="szyfrow.railfence.railfence_decipher"><code class="name flex">
 301 <span>def <span class="ident">railfence_decipher</span></span>(<span>message, height, fillvalue='')</span>
 302 </code></dt>
 303 <dd>
 304 <div class="desc"><p>Railfence decipher.
 305 Works by reconstructing the grid used to generate the ciphertext, then
 306 unfolding the sections so the text can be concatenated together.</p>
 307 <p>Example: given the ciphertext 'hhieterelorfnsled' and a height of 4, first
 308 work out that the second row has a character missing, find the rows of the
 309 grid, then split the section into its two columns.</p>
 310 <p>'hhieterelorfnsled' is split into
 311 h h i
 312 etere
 313 lorfns
 314 l e d
 315 (spaces added for clarity), which is stored in 'rows'. This is then split
 316 into 'down_rows' and 'up_rows':</p>
 317 <p>down_rows:
 318 hhi
 319 eee
 320 lrn
 321 led</p>
 322 <p>up_rows:
 323 tr
 324 ofs</p>
 325 <p>These are then zipped together (after the up_rows are reversed) to recover
 326 the plaintext.</p>
 327 <p>Most of the procedure is about finding the correct lengths for each row then
 328 splitting the ciphertext into those rows.</p>
 329 <pre><code class="language-python-repl">&gt;&gt;&gt; railfence_decipher('hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!', 2).strip('!')
 330 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 331 &gt;&gt;&gt; railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!', 3).strip('!')
 332 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 333 &gt;&gt;&gt; railfence_decipher('hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!', 5).strip('!')
 334 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 335 &gt;&gt;&gt; railfence_decipher('hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!', 10).strip('!')
 336 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 337 &gt;&gt;&gt; railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece', 3)
 338 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 339 &gt;&gt;&gt; railfence_decipher('hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp', 5)
 340 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 341 &gt;&gt;&gt; railfence_decipher('haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic', 7)
 342 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
 343 </code></pre></div>
 344 <details class="source">
 345 <summary>
 346 <span>Expand source code</span>
 347 </summary>
 348 <pre><code class="python">def railfence_decipher(message, height, fillvalue=&#39;&#39;):
 349     &#34;&#34;&#34;Railfence decipher.
 350     Works by reconstructing the grid used to generate the ciphertext, then
 351     unfolding the sections so the text can be concatenated together.
 352
 353     Example: given the ciphertext &#39;hhieterelorfnsled&#39; and a height of 4, first
 354     work out that the second row has a character missing, find the rows of the
 355     grid, then split the section into its two columns.
 356
 357     &#39;hhieterelorfnsled&#39; is split into
 358         h h i
 359         etere
 360         lorfns
 361         l e d
 362     (spaces added for clarity), which is stored in &#39;rows&#39;. This is then split
 363     into &#39;down_rows&#39; and &#39;up_rows&#39;:
 364
 365     down_rows:
 366        hhi
 367        eee
 368        lrn
 369        led
 370
 371     up_rows:
 372        tr
 373        ofs
 374
 375     These are then zipped together (after the up_rows are reversed) to recover
 376     the plaintext.
 377
 378     Most of the procedure is about finding the correct lengths for each row then
 379     splitting the ciphertext into those rows.
 380
 381     &gt;&gt;&gt; railfence_decipher(&#39;hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!&#39;, 2).strip(&#39;!&#39;)
 382     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 383     &gt;&gt;&gt; railfence_decipher(&#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!&#39;, 3).strip(&#39;!&#39;)
 384     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 385     &gt;&gt;&gt; railfence_decipher(&#39;hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!&#39;, 5).strip(&#39;!&#39;)
 386     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 387     &gt;&gt;&gt; railfence_decipher(&#39;hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!&#39;, 10).strip(&#39;!&#39;)
 388     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 389     &gt;&gt;&gt; railfence_decipher(&#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece&#39;, 3)
 390     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 391     &gt;&gt;&gt; railfence_decipher(&#39;hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp&#39;, 5)
 392     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 393     &gt;&gt;&gt; railfence_decipher(&#39;haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic&#39;, 7)
 394     &#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;
 395     &#34;&#34;&#34;
 396     # find the number and size of the sections, including how many characters
 397     #   are missing for a full grid
 398     n_sections = math.ceil(len(message) / ((height - 1) * 2))
 399     padding_to_add = n_sections * (height - 1) * 2 - len(message)
 400     # row_lengths are for the both up rows and down rows
 401     row_lengths = [n_sections] * (height - 1) * 2
 402     for i in range((height - 1) * 2 - 1, (height - 1) * 2 - (padding_to_add + 1), -1):
 403         row_lengths[i] -= 1
 404     # folded_rows are the combined row lengths in the middle of the railfence
 405     folded_row_lengths = [row_lengths[0]]
 406     for i in range(1, height-1):
 407         folded_row_lengths += [row_lengths[i] + row_lengths[-i]]
 408     folded_row_lengths += [row_lengths[height - 1]]
 409     # find the rows that form the railfence grid
 410     rows = []
 411     row_start = 0
 412     for i in folded_row_lengths:
 413         rows += [message[row_start:row_start + i]]
 414         row_start += i
 415     # split the rows into the &#39;down_rows&#39; (those that form the first column of
 416     #   a section) and the &#39;up_rows&#39; (those that ofrm the second column of a
 417     #   section).
 418     down_rows = [rows[0]]
 419     up_rows = []
 420     for i in range(1, height-1):
 421         down_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 0])]
 422         up_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 1])]
 423     down_rows += [rows[-1]]
 424     up_rows.reverse()
 425     return cat(c for r in zip_longest(*(down_rows + up_rows), fillvalue=&#39;&#39;) for c in r)</code></pre>
 426 </details>
 427 </dd>
 428 <dt id="szyfrow.railfence.railfence_encipher"><code class="name flex">
 429 <span>def <span class="ident">railfence_encipher</span></span>(<span>message, height, fillvalue='')</span>
 430 </code></dt>
 431 <dd>
 432 <div class="desc"><p>Railfence cipher.
 433 Works by splitting the text into sections, then reading across them to
 434 generate the rows in the cipher. The rows are then combined to form the
 435 ciphertext.</p>
 436 <p>Example: the plaintext "hellotherefriends", with a height of four, written
 437 out in the railfence as
 438 h h i
 439 etere*
 440 lorfns
 441 l e d
 442 (with the * showing the one character to finish the last section).
 443 Each 'section' is two columns, but unfolded. In the example, the first
 444 section is 'hellot'.</p>
 445 <pre><code class="language-python-repl">&gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 2, fillvalue='!')
 446 'hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!'
 447 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3, fillvalue='!')
 448 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!'
 449 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5, fillvalue='!')
 450 'hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!'
 451 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 10, fillvalue='!')
 452 'hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!'
 453 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3)
 454 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece'
 455 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5)
 456 'hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp'
 457 &gt;&gt;&gt; railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 7)
 458 'haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic'
 459 </code></pre></div>
 460 <details class="source">
 461 <summary>
 462 <span>Expand source code</span>
 463 </summary>
 464 <pre><code class="python">def railfence_encipher(message, height, fillvalue=&#39;&#39;):
 465     &#34;&#34;&#34;Railfence cipher.
 466     Works by splitting the text into sections, then reading across them to
 467     generate the rows in the cipher. The rows are then combined to form the
 468     ciphertext.
 469
 470     Example: the plaintext &#34;hellotherefriends&#34;, with a height of four, written
 471     out in the railfence as
 472        h h i
 473        etere*
 474        lorfns
 475        l e d
 476     (with the * showing the one character to finish the last section).
 477     Each &#39;section&#39; is two columns, but unfolded. In the example, the first
 478     section is &#39;hellot&#39;.
 479
 480     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 2, fillvalue=&#39;!&#39;)
 481     &#39;hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!&#39;
 482     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 3, fillvalue=&#39;!&#39;)
 483     &#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!&#39;
 484     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 5, fillvalue=&#39;!&#39;)
 485     &#39;hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!&#39;
 486     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 10, fillvalue=&#39;!&#39;)
 487     &#39;hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!&#39;
 488     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 3)
 489     &#39;horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece&#39;
 490     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 5)
 491     &#39;hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp&#39;
 492     &gt;&gt;&gt; railfence_encipher(&#39;hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers&#39;, 7)
 493     &#39;haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic&#39;
 494     &#34;&#34;&#34;
 495     sections = chunks(message, (height - 1) * 2, fillvalue=fillvalue)
 496     n_sections = len(sections)
 497     # Add the top row
 498     rows = [cat([s[0] for s in sections])]
 499     # process the middle rows of the grid
 500     for r in range(1, height-1):
 501         rows += [cat([s[r:r+1] + s[height*2-r-2:height*2-r-1] for s in sections])]
 502     # process the bottom row
 503     rows += [cat([s[height - 1:height] for s in sections])]
 504     # rows += [wcat([s[height - 1] for s in sections])]
 505     return cat(rows)</code></pre>
 506 </details>
 507 </dd>
 508 <dt id="szyfrow.railfence.wcat"><code class="name flex">
 509 <span>def <span class="ident">wcat</span></span>(<span>iterable, /)</span>
 510 </code></dt>
 511 <dd>
 512 <div class="desc"><p>Concatenate any number of strings.</p>
 513 <p>The string whose method is called is inserted in between each given string.
 514 The result is returned as a new string.</p>
 515 <p>Example: '.'.join(['ab', 'pq', 'rs']) -&gt; 'ab.pq.rs'</p></div>
 516 </dd>
 517 </dl>
 518 </section>
 519 <section>
 520 </section>
 521 </article>
 522 <nav id="sidebar">
 523 <h1>Index</h1>
 524 <div class="toc">
 525 <ul></ul>
 526 </div>
 527 <ul id="index">
 528 <li><h3>Super-module</h3>
 529 <ul>
 530 <li><code><a title="szyfrow" href="index.html">szyfrow</a></code></li>
 531 </ul>
 532 </li>
 533 <li><h3><a href="#header-functions">Functions</a></h3>
 534 <ul class="two-column">
 535 <li><code><a title="szyfrow.railfence.cat" href="#szyfrow.railfence.cat">cat</a></code></li>
 536 <li><code><a title="szyfrow.railfence.lcat" href="#szyfrow.railfence.lcat">lcat</a></code></li>
 537 <li><code><a title="szyfrow.railfence.railfence_break" href="#szyfrow.railfence.railfence_break">railfence_break</a></code></li>
 538 <li><code><a title="szyfrow.railfence.railfence_decipher" href="#szyfrow.railfence.railfence_decipher">railfence_decipher</a></code></li>
 539 <li><code><a title="szyfrow.railfence.railfence_encipher" href="#szyfrow.railfence.railfence_encipher">railfence_encipher</a></code></li>
 540 <li><code><a title="szyfrow.railfence.wcat" href="#szyfrow.railfence.wcat">wcat</a></code></li>
 541 </ul>
 542 </li>
 543 </ul>
 544 </nav>
 545 </main>
 546 <footer id="footer">
 547 <p>Generated by <a href="https://pdoc3.github.io/pdoc"><cite>pdoc</cite> 0.9.2</a>.</p>
 548 </footer>
 549 </body>
 550 </html>