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diff --git a/python.html.markdown b/python.html.markdown
index 5b36083d..55f56071 100644
--- a/python.html.markdown
+++ b/python.html.markdown
@@ -4,17 +4,26 @@ 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
---
-Python was created by Guido Van Rossum in the early 90s. It is now one of the most popular
-languages in existence. I fell in love with Python for its syntactic clarity. It's basically
-executable pseudocode.
+Python was created by Guido Van Rossum in the early 90s. It is now one of the
+most popular languages in existence. I fell in love with Python for its
+syntactic clarity. It's basically executable pseudocode.
-Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service]
+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
@@ -25,6 +34,7 @@ to Python 2.x. For Python 3.x, take a look at the [Python 3 tutorial](http://lea
as comments
"""
+
####################################################
## 1. Primitive Datatypes and Operators
####################################################
@@ -52,6 +62,12 @@ 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 +126,19 @@ 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")
+# You can find the length of a string
+len("This is a string") # => 16
+
+#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 +155,16 @@ 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
@@ -144,6 +176,12 @@ bool("") # => False
# Python has a print statement
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
some_var # => 5
@@ -153,8 +191,10 @@ 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
li = []
# You can start with a prefilled list
@@ -206,6 +246,17 @@ 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 +277,9 @@ 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
@@ -249,6 +301,9 @@ filled_dict.keys() # => ["three", "two", "one"]
filled_dict.values() # => [3, 2, 1]
# Note - Same as above regarding key ordering.
+# Get all key-value pairs as a list of tuples with "items()"
+filled_dicts.items() # => [("one", 1), ("two", 2), ("three", 3)]
+
# Check for existence of keys in a dictionary with "in"
"one" in filled_dict # => True
1 in filled_dict # => False
@@ -297,6 +352,15 @@ 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
@@ -387,6 +451,7 @@ with open("myfile.txt") as f:
for line in f:
print line
+
####################################################
## 4. Functions
####################################################
@@ -404,15 +469,14 @@ 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 if you do not use the *
+# positional args, which will be interpreted as a tuple by using *
def varargs(*args):
return args
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 if you do not use **
+# keyword args, as well, which will be interpreted as a dict by using **
def keyword_args(**kwargs):
return kwargs
@@ -448,19 +512,19 @@ 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):
@@ -485,6 +549,10 @@ filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
+# You can construct set and dict comprehensions as well.
+{x for x in 'abcddeef' if x in 'abc'} # => {'d', 'e', 'f'}
+{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
+
####################################################
## 5. Classes
@@ -504,6 +572,10 @@ 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)
@@ -519,6 +591,23 @@ 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")
@@ -538,6 +627,16 @@ 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
@@ -572,34 +671,67 @@ math.sqrt == m.sqrt == sqrt # => True
import math
dir(math)
+# If you have a Python script named math.py in the same
+# folder as your current script, the file math.py will
+# be loaded instead of the built-in Python module.
+# This happens because the local folder has priority
+# over Python's built-in libraries.
+
####################################################
## 7. Advanced
####################################################
-# Generators help you make lazy code
+# Generators
+# A generator "generates" values as they are requested instead of storing
+# everything up front
+
+# The following method (*NOT* a generator) will double all values and store it
+# in `double_arr`. For large size of iterables, that might get huge!
def double_numbers(iterable):
+ double_arr = []
+ for i in iterable:
+ double_arr.append(i + i)
+
+# Running the following would mean we'll double all values first and return all
+# of them back to be checked by our condition
+for value in double_numbers(range(1000000)): # `test_non_generator`
+ print value
+ if value > 5:
+ break
+
+# We could instead use a generator to "generate" the doubled value as the item
+# is being requested
+def double_numbers_generator(iterable):
for i in iterable:
yield i + i
-# A generator creates values on the fly.
-# Instead of generating and returning all values at once it creates one in each
-# iteration. This means values bigger than 15 wont be processed in
-# double_numbers.
-# Note xrange is a generator that does the same thing range does.
-# Creating a list 1-900000000 would take lot of time and space to be made.
-# xrange creates an xrange generator object instead of creating the entire list
-# like range does.
-# We use a trailing underscore in variable names when we want to use a name that
-# would normally collide with a python keyword
-xrange_ = xrange(1, 900000000)
-
-# will double all numbers until a result >=30 found
-for i in double_numbers(xrange_):
- print i
- if i >= 30:
+# Running the same code as before, but with a generator, now allows us to iterate
+# over the values and doubling them one by one as they are being consumed by
+# our logic. Hence as soon as we see a value > 5, we break out of the
+# loop and don't need to double most of the values sent in (MUCH FASTER!)
+for value in double_numbers_generator(xrange(1000000)): # `test_generator`
+ print value
+ if value > 5:
break
+# BTW: did you notice the use of `range` in `test_non_generator` and `xrange` in `test_generator`?
+# Just as `double_numbers_generator` is the generator version of `double_numbers`
+# We have `xrange` as the generator version of `range`
+# `range` would return back and array with 1000000 values for us to use
+# `xrange` would generate 1000000 values for us as we request / iterate over those items
+
+# Just as you can create a list comprehension, you can create generator
+# comprehensions as well.
+values = (-x for x in [1,2,3,4,5])
+for x in values:
+ print(x) # prints -1 -2 -3 -4 -5 to console/terminal
+
+# You can also cast a generator comprehension directly to a list.
+values = (-x for x in [1,2,3,4,5])
+gen_to_list = list(values)
+print(gen_to_list) # => [-1, -2, -3, -4, -5]
+
# Decorators
# in this example beg wraps say
@@ -607,7 +739,6 @@ for i in double_numbers(xrange_):
# message
from functools import wraps
-
def beg(target_function):
@wraps(target_function)
def wrapper(*args, **kwargs):
@@ -618,13 +749,11 @@ def beg(target_function):
return wrapper
-
@beg
def say(say_please=False):
msg = "Can you buy me a beer?"
return msg, say_please
-
print say() # Can you buy me a beer?
print say(say_please=True) # Can you buy me a beer? Please! I am poor :(
```
@@ -636,11 +765,13 @@ 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)
* [First Steps With Python](https://realpython.com/learn/python-first-steps/)
+* [LearnPython](http://www.learnpython.org/)
+* [Fullstack Python](https://www.fullstackpython.com/)
### Dead Tree