Master slice in python (#26)

* [ADD] Blog post discussing the reasons for returning an empty list instead of raising an IndexError from slice function.

Author: ultimatecoder

Gemfile.lock

@@ -1,33 +1,34 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (5.1.0)
+    activesupport (5.2.1)
       concurrent-ruby (~> 1.0, >= 1.0.2)
-      i18n (~> 0.7)
+      i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
-    addressable (2.5.0)
-      public_suffix (~> 2.0, >= 2.0.2)
+    addressable (2.5.2)
+      public_suffix (>= 2.0.2, < 4.0)
     colorator (1.1.0)
-    colored (1.2)
+    colorize (0.8.1)
     concurrent-ruby (1.0.5)
     cssminify2 (2.0.1)
-    ethon (0.10.1)
+    ethon (0.11.0)
       ffi (>= 1.3.0)
     execjs (2.7.0)
-    ffi (1.9.14)
+    ffi (1.9.25)
     forwardable-extended (2.6.0)
-    html-proofer (3.6.0)
+    html-proofer (3.9.2)
       activesupport (>= 4.2, < 6.0)
       addressable (~> 2.3)
-      colored (~> 1.2)
+      colorize (~> 0.8)
       mercenary (~> 0.3.2)
-      nokogiri (~> 1.5)
+      nokogiri (~> 1.8.1)
       parallel (~> 1.3)
-      typhoeus (~> 0.7)
+      typhoeus (~> 1.3)
       yell (~> 2.0)
-    htmlcompressor (0.3.1)
-    i18n (0.8.1)
+    htmlcompressor (0.4.0)
+    i18n (1.1.0)
+      concurrent-ruby (~> 1.0)
     jekyll (3.3.1)
       addressable (~> 2.4)
       colorator (~> 1.0)
@@ -39,48 +40,54 @@ GEM
       pathutil (~> 0.9)
       rouge (~> 1.7)
       safe_yaml (~> 1.0)
-    jekyll-feed (0.8.0)
+    jekyll-feed (0.11.0)
       jekyll (~> 3.3)
     jekyll-minifier (0.1.2)
       cssminify2 (~> 2.0)
       htmlcompressor (~> 0.3)
       jekyll (~> 3.0)
       uglifier (~> 2.7)
-    jekyll-sass-converter (1.5.0)
+    jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-seo-tag (2.2.3)
+    jekyll-seo-tag (2.5.0)
       jekyll (~> 3.3)
-    jekyll-sitemap (1.1.1)
+    jekyll-sitemap (1.2.0)
       jekyll (~> 3.3)
-    jekyll-watch (1.5.0)
-      listen (~> 3.0, < 3.1)
+    jekyll-watch (1.5.1)
+      listen (~> 3.0)
     json (2.1.0)
-    kramdown (1.13.1)
+    kramdown (1.17.0)
     liquid (3.0.6)
-    listen (3.0.8)
+    listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+      ruby_dep (~> 1.2)
     mercenary (0.3.6)
-    mini_portile2 (2.1.0)
-    minima (2.1.0)
+    mini_portile2 (2.3.0)
+    minima (2.1.1)
       jekyll (~> 3.3)
-    minitest (5.10.1)
-    nokogiri (1.7.1)
-      mini_portile2 (~> 2.1.0)
-    parallel (1.11.2)
-    pathutil (0.14.0)
+    minitest (5.11.3)
+    nokogiri (1.8.4)
+      mini_portile2 (~> 2.3.0)
+    parallel (1.12.1)
+    pathutil (0.16.1)
       forwardable-extended (~> 2.6)
-    public_suffix (2.0.4)
-    rb-fsevent (0.9.8)
-    rb-inotify (0.9.7)
-      ffi (>= 0.5.0)
+    public_suffix (3.0.3)
+    rb-fsevent (0.10.3)
+    rb-inotify (0.9.10)
+      ffi (>= 0.5.0, < 2)
     rouge (1.11.1)
+    ruby_dep (1.5.0)
     safe_yaml (1.0.4)
-    sass (3.4.23)
+    sass (3.6.0)
+      sass-listen (~> 4.0.0)
+    sass-listen (4.0.0)
+      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-inotify (~> 0.9, >= 0.9.7)
     thread_safe (0.3.6)
-    typhoeus (0.8.0)
-      ethon (>= 0.8.0)
-    tzinfo (1.2.3)
+    typhoeus (1.3.0)
+      ethon (>= 0.9.0)
+    tzinfo (1.2.5)
       thread_safe (~> 0.1)
     uglifier (2.7.2)
       execjs (>= 0.3.0)
@@ -100,7 +107,7 @@ DEPENDENCIES
   minima (~> 2.0)
 
 RUBY VERSION
-   ruby 2.3.1p112
+   ruby 2.3.7p456
 
 BUNDLED WITH
-   1.13.7
+   1.16.5

_posts/2018-09-29-analyzing-the-behaviour-of-python-function-splice.md

@@ -0,0 +1,155 @@
+---
+layout: post
+title: "Analyzing the behaviour of Python function slice"
+date: "2018-09-29 10:17:46 +0530"
+tag:
+  - python
+  - slice
+  - python trick questions
+---
+
+
+![Title Image](/assets/images/python_slice_function/title_image.jpg)
+
+Last Friday, I was sitting in one of the good coffee shops in Bangalore with my
+friend. Coffee and discussion is the best combination to release stress. It was
+looking like a perfect Friday evening until my friend was struck by an idea of
+asking me a question.
+
+“Let me conduct a quiz.” he said, interrupting our conversation.
+
+“A quiz? Quiz on what?”, I asked.
+
+“On programming”, he said
+
+“What is the level of difficulty then?” I said.
+
+Asking the level of difficulty is important. I never invest my efforts in
+solving something easy. If he had said easy, I would have ignored to answer, but
+he said “It is a bit difficult, but not that difficult. I gave a wrong answer to
+this question in my last interview.”
+
+There was no reason to go back from here. Taking some deep breaths I said,
+“Please go ahead.”
+
+He stood up, took a tissue paper from a nearby counter and scratched below code
+on it. [^1] And he asked me by pointing towards that code, “What will be the output
+of this code?”
+
+```python
+def my_function():
+    l = [0, 1, 2]
+    print(l[30:])
+
+my_function()
+```
+
+Now it was my turn to give the answer. I looked at the code and tried parsing it
+in my head --- line by line. In my mind, I observed the first line. It was
+defining a function which seems to be correct. I moved my eyes to the next line.
+It was defining a variable `l` of type `list` and assigning values ranging from
+`0` to `2`.  Even this wasn’t looking problematic. So I forwarded to the next
+line where it was trying to print that variable `l` by slicing it from starting
+value `30` to the infinity.
+
+“Well, the start value is `30` which is greater than the length of the list.
+This should raise an `IndexError`” I said in my mind. I was about to speak an
+answer, but suddenly Devil of me flashed.
+
+“It is less than [a banana job][4] my dear,” the Devil said to me, “You should
+take a little advantage of this opportunity my boy.”
+
+Because things were looking in my control, I shook my hands with the Devil.
+
+I said to my friend, “How about betting for some real values?”
+
+Going closer I spoke, “If I answer correctly, You will pay the bill and If I am
+wrong, This will be a treat from my side.”
+
+He thought for a while and nodded. Now it was my turn to unveil the cards.
+
+I said in a strong voice, “It will raise an `IndexError`.” And shifted my focus
+towards the chocolate.
+
+He starred my face for a second and spoke, “Okay. Are you sure about this?”.
+
+This was the hint he gave. I should have taken another shot here.  What happens
+next become a lesson for me.
+
+I said with a flat face, “Yes I am.”
+
+With my answer, he instantly opened his backpack, took his Laptop out and typed
+the code which he wrote on that tissue.
+
+When I stopped hearing a sound of typing I yelled, “So did I win?”
+
+He turned his laptop towards me and exclaimed, “Not at all!”
+
+When I focused on the screen, the interpreter was printing `[]`. Damn! I lost
+the bet.  Why the hell `slice` is returning an empty `list` even when we are
+trying to slice it with a value which is greater than the length of it! It was
+surely looking unpythonic behavior. I paid whatever the bill amount was. Entire
+evening this question was all roaming my mind. After coming home, I decided to
+justify reasons for returning an empty list instead of raising an `IndexError`
+from a `slice`.
+
+Below are a few reasons justifying such behavior of slice function. I am sharing
+this with you so that you don’t lose a bet with your friend :) For those who
+haven’t used slice anytime in their life, I advise to read [this][1] tutorial.
+Reading [this][2] guide for understanding how a slice function converts the
+input values. Especially rule number 3 and 4 referenced there.
+
+* **Reason number one:**
+
+  Python lists are more commonly used in iterations. Consider below example:
+
+  ```python
+  numbers = [0, 1, 2, 3]
+  for number in numbers[30:]:
+      print(number)
+  ```
+
+  If `slice` was raising an `IndexError`, then the above code would have to
+  written like this
+
+  written like like this
+
+  ```python
+  numbers = [0, 1, 2, 3]
+  try:
+      for number in numbers[30:]:
+          print(numbers)
+  except IndexError:
+      pass
+  ```
+
+  Or in another way below is also looking reasonable
+
+  ```python
+  numbers = [0, 1, 2, 3]
+  start = 30
+  if start < len(numbers):
+      for number in numbers[start:]:
+          print(number)
+  ```
+
+  Both the approaches are looking little lengthy by an obvious reason. And that
+  reason is to prevent executing loop if there are no elements in it.  When we
+  observe the behavior of `slice` called at `for in`, it makes sense to return
+  an empty list instead of raising an `IndexError`.
+
+I am not able to find further reasons to return an empty list instead of raising
+the `IndexError`. But I am sure, there will be. If you know any other potential
+reasons for such behavior of `slice`, please drop me a mail at **jaysinhp** at
+**gmail** dot **com** or contact me over Twitter [@jaysinhp][3].  I will update
+the reasons at this post and give credits to you. Thanks for reading this post.
+
+
+###### Proofreaders: [Geoffrey Sneddon](https://github.com/gsnedders), [Elijah](https://mailto:[email protected]), [Mahendra Yadav](mailto:[email protected]), [Dhavan Vaidya](http://codingquark.com/),
+
+[1]: https://docs.python.org/3.7/tutorial/introduction.html#lists
+[2]: https://docs.python.org/3.7/library/stdtypes.html#sequence-types-list-tuple-range
+[3]: https://twitter.com/jaysinhp
+[4]: http://catb.org/jargon/html/O/one-banana-problem.html
+
+[^1]: I am using the word "Scratch" because that tissue paper was such a thin that writing by a ballpen torn it.