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--- python_notes [2023/05/19 20:27] – [read file into a list] admin
+++ python_notes [2023/12/31 19:54] – [List of comparison operators] raju
@@ Line 2: / Line 2: @@
 ==== useful links ====
+  * [[https://tutswiki.com/python/exception-handling/ | exception handling in python]] (tutswiki.com)
+    * very easy to follow; high information density; well thought out examples
   * [[https://www.programiz.com/python-programming/online-compiler/ | Online python compiler]] (programiz.com)
     * can be useful while doing live coding interviews.
@@ Line 115: / Line 117: @@
 </code>
+==== check if something is float ====
+<code>
+% python
+Python 3.11.4 (main, Jul  5 2023, 13:45:01) [GCC 11.2.0] on linux
+Type "help", "copyright", "credits" or "license" for more information.
+>>> isinstance(12.0, float)
+True
+>>> isinstance(12.0, int)
+False
+>>> isinstance(12, float)
+False
+</code>
+==== check if something is int ====
+<code>
+% python
+Python 3.11.4 (main, Jul  5 2023, 13:45:01) [GCC 11.2.0] on linux
+Type "help", "copyright", "credits" or "license" for more information.
+>>> isinstance(12, int)
+True
+>>> isinstance(12, float)
+False
+>>> isinstance(12.0, int)
+False
+</code>
+==== Python comparisons ====
+<code>
+$ python
+Python 3.9.17 (main, Jul  5 2023, 20:47:11) [MSC v.1916 64 bit (AMD64)] on win32
+Type "help", "copyright", "credits" or "license" for more information.
+>>> 4 == True
+False
+>>> 1 == True
+True
+</code>
+==== Chained comparisons ====
+Q: In Python ''3 < 4 == True'' evaluates to False.
+<code>
+$ python
+Python 3.9.17 (main, Jul  5 2023, 20:47:11) [MSC v.1916 64 bit (AMD64)] on win32
+Type "help", "copyright", "credits" or "license" for more information.
+>>> 3 < 4 == True
+False
+</code>
+Why?
+A: The ''<'' and ''=='' are comparison operators. If a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then in python, a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.
+So ''3 < 4 == True'' is equivalent to ''3 < 4 and 4 == True'' which evaluates to ''True and False'' which turns out to be ''False''.
+Ref:-
+  * https://docs.python.org/3/reference/expressions.html#comparisons - describes the above rule and also gives a list of comparison operators
+==== List of comparison operators ====
+<code>
+"<" | ">" | "==" | ">=" | "<=" | "!="
+| "is" ["not"] | ["not"] "in"
+</code>
+Ref:- https://docs.python.org/3/reference/expressions.html#comparisons
 ===== tasks =====
   * [[get urls in a url]]
@@ Line 121: / Line 187: @@
 ===== difference between =====
+==== os.getenv vs. os.environ.get ====
+What is the difference between os.getenv vs os.environ.get?
+None. I prefer to use os.getenv as it is less number of characters to type.
+To experiment, use [[https://github.com/KamarajuKusumanchi/notebooks/blob/master/python/difference%20between%20os.getenv%20vs.%20os.environ.get.ipynb | difference between os.getenv vs. os.environ.get.ipynb]] (github.com/KamarajuKusumanchi).
+Sample usage from https://github.com/dpguthrie/yahooquery/blob/master/yahooquery/base.py#LL926C1-L936C1
+<code>
+    def __init__(self, **kwargs):
+        ...
+        username = os.getenv("YF_USERNAME") or kwargs.get("username")
+        password = os.getenv("YF_PASSWORD") or kwargs.get("password")
+        if username and password:
+            self.login(username, password)
+</code>
 ===== Snippets =====
@@ Line 193: / Line 274: @@
 ===== Reading files =====
 ==== read file into a list ====
+Given
 <code>
-$ cat great.txt
+$ cat -A great.txt
-kamaraju
+kamaraju$
-kamaraj
+kamaraj $
-kamara
+kamara  $
-kamar
+kamar   $
-kama
+kama    $
-kam
+kam     $
-ka
+ka      $
-k
+k       $
 </code>
+where the $ denotes the end of line.
+<code>
+$ du -b great.txt
+      great.txt
+$ wc great.txt
+  8 72 great.txt
+</code>
+To read it
 <code>
-In [2]: file = 'great.txt'
+In [3]:
-   ...: with open(file) as fh:
+file = 'great.txt'
-   ...:     contents = [line.rstrip() for line in fh]
+with open(file) as fh:
-   ...: print(contents)
+    contents = [line.rstrip('\n') for line in fh]
-['kamaraju', 'kamaraj', 'kamara', 'kamar', 'kama', 'kam', 'ka', 'k']
+print(contents)
+['kamaraju', 'kamaraj ', 'kamara  ', 'kamar   ', 'kama    ', 'kam     ', 'ka      ', 'k       ']
-In [3]: len(contents)
+In [4]:
-Out[3]: 8
+len(contents)
+Out[4]:
 </code>
 Ref:- https://stackoverflow.com/questions/15233340/getting-rid-of-n-when-using-readlines
-If you use readlines(), there will be a new line character at the end.
+You can also do it using readlines.
+<code>
+In [5]:
+file = 'great.txt'
+with open(file) as fh:
+    lines = fh.readlines()
+    lines = [line.rstrip('\n') for line in lines]
+print(lines)
+['kamaraju', 'kamaraj ', 'kamara  ', 'kamar   ', 'kama    ', 'kam     ', 'ka      ', 'k       ']
+</code>
+tags | file readlines strip newline
+Another approach is to use read() with splitlines().
+<code>
+In [6]:
+file = 'great.txt'
+with open(file) as fh:
+    lines = fh.read().splitlines()
+print(lines)
+['kamaraju', 'kamaraj ', 'kamara  ', 'kamar   ', 'kama    ', 'kam     ', 'ka      ', 'k       ']
+</code>
+===== programming notes =====
+==== which python executable am I running? ====
+<code>
+import sys
+print(sys.executable)
+</code>
+For example
 <code>
-In [4]: file = 'great.txt'
+$ python
-   ...: with open(file) as fh:
+Python 3.11.5 | packaged by Anaconda, Inc. | (main, Sep 11 2023, 13:26:23) [MSC v.1916 64 bit (AMD64)] on win32
-   ...:     contents = fh.readlines()
+Type "help", "copyright", "credits" or "license" for more information.
-   ...: print(contents)
+>>> import sys
-['kamaraju\n', 'kamaraj\n', 'kamara\n', 'kamar\n', 'kama\n', 'kam\n', 'ka\n', 'k\n']
+>>> print(sys.executable)
+C:\Users\kkusuman\AppData\Local\conda\conda\envs\py311\python.exe
 </code>