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Merged and removed confusing comments in python

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Aayush Ranaut
2015-12-05 11:10:16 +05:30
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@@ -4,6 +4,7 @@ contributors:
- ["Louie Dinh", "http://ldinh.ca"]
- ["Amin Bandali", "http://aminbandali.com"]
- ["Andre Polykanine", "https://github.com/Oire"]
- ["evuez", "http://github.com/evuez"]
filename: learnpython.py
---
@@ -14,7 +15,13 @@ executable pseudocode.
Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service]
Note: This article applies to Python 2.7 specifically, but should be applicable
to Python 2.x. For Python 3.x, take a look at the [Python 3 tutorial](http://learnxinyminutes.com/docs/python3/).
to Python 2.x. Python 2.7 is reaching end of life and will stop being maintained in 2020,
it is though recommended to start learning Python with Python 3.
For Python 3.x, take a look at the [Python 3 tutorial](http://learnxinyminutes.com/docs/python3/).
It is also possible to write Python code which is compatible with Python 2.7 and 3.x at the same time,
using Python [`__future__` imports](https://docs.python.org/2/library/__future__.html). `__future__` imports
allow you to write Python 3 code that will run on Python 2, so check out the Python 3 tutorial.
```python
@@ -52,6 +59,12 @@ to Python 2.x. For Python 3.x, take a look at the [Python 3 tutorial](http://lea
-5 // 3 # => -2
-5.0 // 3.0 # => -2.0
# Note that we can also import division module(Section 6 Modules)
# to carry out normal division with just one '/'.
from __future__ import division
11/4 # => 2.75 ...normal division
11//4 # => 2 ...floored division
# Modulo operation
7 % 3 # => 1
@@ -110,11 +123,16 @@ not False # => True
# A string can be treated like a list of characters
"This is a string"[0] # => 'T'
# % can be used to format strings, like this:
"%s can be %s" % ("strings", "interpolated")
#String formatting with %
#Even though the % string operator will be deprecated on Python 3.1 and removed
#later at some time, it may still be good to know how it works.
x = 'apple'
y = 'lemon'
z = "The items in the basket are %s and %s" % (x,y)
# A newer way to format strings is the format method.
# This method is the preferred way
"{} is a {}".format("This", "placeholder")
"{0} can be {1}".format("strings", "formatted")
# You can use keywords if you don't want to count.
"{name} wants to eat {food}".format(name="Bob", food="lasagna")
@@ -131,8 +149,16 @@ None is None # => True
# very useful when dealing with primitive values, but is
# very useful when dealing with objects.
# None, 0, and empty strings/lists all evaluate to False.
# All other values are True
# Any object can be used in a Boolean context.
# The following values are considered falsey:
# - None
# - zero of any numeric type (e.g., 0, 0L, 0.0, 0j)
# - empty sequences (e.g., '', (), [])
# - empty containers (e.g., {}, set())
# - instances of user-defined classes meeting certain conditions
# see: https://docs.python.org/2/reference/datamodel.html#object.__nonzero__
#
# All other values are truthy (using the bool() function on them returns True).
bool(0) # => False
bool("") # => False
@@ -142,7 +168,13 @@ bool("") # => False
####################################################
# Python has a print statement
print "I'm Python. Nice to meet you!"
print "I'm Python. Nice to meet you!" # => I'm Python. Nice to meet you!
# Simple way to get input data from console
input_string_var = raw_input("Enter some data: ") # Returns the data as a string
input_var = input("Enter some data: ") # Evaluates the data as python code
# Warning: Caution is recommended for input() method usage
# Note: In python 3, input() is deprecated and raw_input() is renamed to input()
# No need to declare variables before assigning to them.
some_var = 5 # Convention is to use lower_case_with_underscores
@@ -153,6 +185,7 @@ some_var # => 5
some_other_var # Raises a name error
# if can be used as an expression
# Equivalent of C's '?:' ternary operator
"yahoo!" if 3 > 2 else 2 # => "yahoo!"
# Lists store sequences
@@ -206,6 +239,17 @@ li + other_li # => [1, 2, 3, 4, 5, 6]
# Concatenate lists with "extend()"
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
# Remove first occurrence of a value
li.remove(2) # li is now [1, 3, 4, 5, 6]
li.remove(2) # Raises a ValueError as 2 is not in the list
# Insert an element at a specific index
li.insert(1, 2) # li is now [1, 2, 3, 4, 5, 6] again
# Get the index of the first item found
li.index(2) # => 1
li.index(7) # Raises a ValueError as 7 is not in the list
# Check for existence in a list with "in"
1 in li # => True
@@ -226,8 +270,9 @@ tup[:2] # => (1, 2)
# You can unpack tuples (or lists) into variables
a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
d, e, f = 4, 5, 6 # you can leave out the parentheses
# Tuples are created by default if you leave out the parentheses
d, e, f = 4, 5, 6
g = 4, 5, 6 # => (4, 5, 6)
# Now look how easy it is to swap two values
e, d = d, e # d is now 5 and e is now 4
@@ -297,6 +342,15 @@ filled_set | other_set # => {1, 2, 3, 4, 5, 6}
# Do set difference with -
{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
# Do set symmetric difference with ^
{1, 2, 3, 4} ^ {2, 3, 5} # => {1, 4, 5}
# Check if set on the left is a superset of set on the right
{1, 2} >= {1, 2, 3} # => False
# Check if set on the left is a subset of set on the right
{1, 2} <= {1, 2, 3} # => True
# Check for existence in a set with in
2 in filled_set # => True
10 in filled_set # => False
@@ -404,7 +458,7 @@ add(y=6, x=5) # Keyword arguments can arrive in any order.
# You can define functions that take a variable number of
# positional args, which will be interpreted as a tuple
# positional args, which will be interpreted as a tuple by using *
def varargs(*args):
return args
@@ -412,7 +466,7 @@ varargs(1, 2, 3) # => (1, 2, 3)
# You can define functions that take a variable number of
# keyword args, as well, which will be interpreted as a dict
# keyword args, as well, which will be interpreted as a dict by using **
def keyword_args(**kwargs):
return kwargs
@@ -448,19 +502,19 @@ def pass_all_the_args(*args, **kwargs):
# Function Scope
x = 5
def setX(num):
def set_x(num):
# Local var x not the same as global variable x
x = num # => 43
print x # => 43
def setGlobalX(num):
def set_global_x(num):
global x
print x # => 5
x = num # global var x is now set to 6
print x # => 6
setX(43)
setGlobalX(6)
set_x(43)
set_global_x(6)
# Python has first class functions
def create_adder(x):
@@ -473,9 +527,12 @@ add_10(3) # => 13
# There are also anonymous functions
(lambda x: x > 2)(3) # => True
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
# There are built-in higher order functions
map(add_10, [1, 2, 3]) # => [11, 12, 13]
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
# We can use list comprehensions for nice maps and filters
@@ -501,6 +558,10 @@ class Human(object):
# Assign the argument to the instance's name attribute
self.name = name
# Initialize property
self.age = 0
# An instance method. All methods take "self" as the first argument
def say(self, msg):
return "{0}: {1}".format(self.name, msg)
@@ -516,6 +577,23 @@ class Human(object):
def grunt():
return "*grunt*"
# A property is just like a getter.
# It turns the method age() into an read-only attribute
# of the same name.
@property
def age(self):
return self._age
# This allows the property to be set
@age.setter
def age(self, age):
self._age = age
# This allows the property to be deleted
@age.deleter
def age(self):
del self._age
# Instantiate a class
i = Human(name="Ian")
@@ -535,6 +613,16 @@ j.get_species() # => "H. neanderthalensis"
# Call the static method
Human.grunt() # => "*grunt*"
# Update the property
i.age = 42
# Get the property
i.age # => 42
# Delete the property
del i.age
i.age # => raises an AttributeError
####################################################
## 6. Modules
@@ -633,7 +721,7 @@ print say(say_please=True) # Can you buy me a beer? Please! I am poor :(
* [Automate the Boring Stuff with Python](https://automatetheboringstuff.com)
* [Learn Python The Hard Way](http://learnpythonthehardway.org/book/)
* [Dive Into Python](http://www.diveintopython.net/)
* [The Official Docs](http://docs.python.org/2.6/)
* [The Official Docs](http://docs.python.org/2/)
* [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/)
* [Python Module of the Week](http://pymotw.com/2/)
* [A Crash Course in Python for Scientists](http://nbviewer.ipython.org/5920182)