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-rw-r--r--python.html.markdown138
1 files changed, 94 insertions, 44 deletions
diff --git a/python.html.markdown b/python.html.markdown
index 9057dde2..ace3f794 100644
--- a/python.html.markdown
+++ b/python.html.markdown
@@ -3,24 +3,25 @@ language: python
contributors:
- ["Louie Dinh", "http://ldinh.ca"]
- ["Amin Bandali", "http://aminbandali.com"]
+ - ["Andre Polykanine", "https://github.com/Oire"]
filename: learnpython.py
---
-Python was created by Guido Van Rossum in the early 90's. It is now one of the most popular
+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]
Note: This article applies to Python 2.7 specifically, but should be applicable
-to Python 2.x. Look for another tour of Python 3 soon!
+to Python 2.x. For Python 3.x, take a look at the [Python 3 tutorial](http://learnxinyminutes.com/docs/python3/).
```python
# Single line comments start with a number symbol.
""" Multiline strings can be written
- using three "'s, and are often used
+ using three "s, and are often used
as comments
"""
@@ -45,7 +46,7 @@ to Python 2.x. Look for another tour of Python 3 soon!
2.0 # This is a float
11.0 / 4.0 # => 2.75 ahhh...much better
-# Result of integer division truncated down both for positive and negative.
+# Result of integer division truncated down both for positive and negative.
5 // 3 # => 1
5.0 // 3.0 # => 1.0 # works on floats too
-5 // 3 # => -2
@@ -54,12 +55,23 @@ to Python 2.x. Look for another tour of Python 3 soon!
# Modulo operation
7 % 3 # => 1
+# Exponentiation (x to the yth power)
+2**4 # => 16
+
# Enforce precedence with parentheses
(1 + 3) * 2 # => 8
-# Boolean values are primitives
-True
-False
+# Boolean Operators
+# Note "and" and "or" are case-sensitive
+True and False #=> False
+False or True #=> True
+
+# Note using Bool operators with ints
+0 and 2 #=> 0
+-5 or 0 #=> -5
+0 == False #=> True
+2 == True #=> False
+1 == True #=> True
# negate with not
not True # => False
@@ -89,6 +101,11 @@ not False # => True
# Strings can be added too!
"Hello " + "world!" # => "Hello world!"
+# Strings can be added without using '+'
+"Hello " "world!" # => "Hello world!"
+
+# ... or multiplied
+"Hello" * 3 # => "HelloHelloHello"
# A string can be treated like a list of characters
"This is a string"[0] # => 'T'
@@ -124,11 +141,8 @@ bool("") # => False
## 2. Variables and Collections
####################################################
-# Python has a print function, available in versions 2.7 and 3...
-print("I'm Python. Nice to meet you!")
-# and an older print statement, in all 2.x versions but removed from 3.
-print "I'm also Python!"
-
+# Python has a print statement
+print "I'm Python. Nice to meet you!"
# No need to declare variables before assigning to them.
some_var = 5 # Convention is to use lower_case_with_underscores
@@ -158,6 +172,10 @@ li.append(3) # li is now [1, 2, 4, 3] again.
# Access a list like you would any array
li[0] # => 1
+# Assign new values to indexes that have already been initialized with =
+li[0] = 42
+li[0] # => 42
+li[0] = 1 # Note: setting it back to the original value
# Look at the last element
li[-1] # => 3
@@ -173,16 +191,17 @@ li[2:] # => [4, 3]
li[:3] # => [1, 2, 4]
# Select every second entry
li[::2] # =>[1, 4]
-# Revert the list
+# Reverse a copy of the list
li[::-1] # => [3, 4, 2, 1]
# Use any combination of these to make advanced slices
# li[start:end:step]
# Remove arbitrary elements from a list with "del"
del li[2] # li is now [1, 2, 3]
-
+r
# You can add lists
-li + other_li # => [1, 2, 3, 4, 5, 6] - Note: values for li and for other_li are not modified.
+li + other_li # => [1, 2, 3, 4, 5, 6]
+# Note: values for li and for other_li are not modified.
# Concatenate lists with "extend()"
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
@@ -243,17 +262,25 @@ filled_dict.get("four") # => None
# The get method supports a default argument when the value is missing
filled_dict.get("one", 4) # => 1
filled_dict.get("four", 4) # => 4
+# note that filled_dict.get("four") is still => None
+# (get doesn't set the value in the dictionary)
+
+# set the value of a key with a syntax similar to lists
+filled_dict["four"] = 4 # now, filled_dict["four"] => 4
# "setdefault()" inserts into a dictionary only if the given key isn't present
filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5
filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5
-# Sets store ... well sets
+# Sets store ... well sets (which are like lists but can contain no duplicates)
empty_set = set()
# Initialize a "set()" with a bunch of values
some_set = set([1, 2, 2, 3, 4]) # some_set is now set([1, 2, 3, 4])
+# order is not guaranteed, even though it may sometimes look sorted
+another_set = set([4, 3, 2, 2, 1]) # another_set is now set([1, 2, 3, 4])
+
# Since Python 2.7, {} can be used to declare a set
filled_set = {1, 2, 2, 3, 4} # => {1, 2, 3, 4}
@@ -285,11 +312,11 @@ some_var = 5
# Here is an if statement. Indentation is significant in python!
# prints "some_var is smaller than 10"
if some_var > 10:
- print("some_var is totally bigger than 10.")
+ print "some_var is totally bigger than 10."
elif some_var < 10: # This elif clause is optional.
- print("some_var is smaller than 10.")
+ print "some_var is smaller than 10."
else: # This is optional too.
- print("some_var is indeed 10.")
+ print "some_var is indeed 10."
"""
@@ -301,7 +328,7 @@ prints:
"""
for animal in ["dog", "cat", "mouse"]:
# You can use % to interpolate formatted strings
- print("%s is a mammal" % animal)
+ print "%s is a mammal" % animal
"""
"range(number)" returns a list of numbers
@@ -313,7 +340,19 @@ prints:
3
"""
for i in range(4):
- print(i)
+ print i
+
+"""
+"range(lower, upper)" returns a list of numbers
+from the lower number to the upper number
+prints:
+ 4
+ 5
+ 6
+ 7
+"""
+for i in range(4, 8):
+ print i
"""
While loops go until a condition is no longer met.
@@ -325,7 +364,7 @@ prints:
"""
x = 0
while x < 4:
- print(x)
+ print x
x += 1 # Shorthand for x = x + 1
# Handle exceptions with a try/except block
@@ -348,7 +387,7 @@ else: # Optional clause to the try/except block. Must follow all except blocks
# Use "def" to create new functions
def add(x, y):
- print("x is %s and y is %s" % (x, y))
+ print "x is %s and y is %s" % (x, y)
return x + y # Return values with a return statement
# Calling functions with parameters
@@ -359,7 +398,7 @@ add(y=6, x=5) # Keyword arguments can arrive in any order.
# You can define functions that take a variable number of
-# positional arguments
+# positional args, which will be interpreted as a tuple if you do not use the *
def varargs(*args):
return args
@@ -367,7 +406,7 @@ varargs(1, 2, 3) # => (1, 2, 3)
# You can define functions that take a variable number of
-# keyword arguments, as well
+# keyword args, as well, which will be interpreted as a map if you do not use **
def keyword_args(**kwargs):
return kwargs
@@ -377,8 +416,8 @@ keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
# You can do both at once, if you like
def all_the_args(*args, **kwargs):
- print(args)
- print(kwargs)
+ print args
+ print kwargs
"""
all_the_args(1, 2, a=3, b=4) prints:
(1, 2)
@@ -386,26 +425,33 @@ all_the_args(1, 2, a=3, b=4) prints:
"""
# When calling functions, you can do the opposite of args/kwargs!
-# Use * to expand tuples and use ** to expand kwargs.
+# Use * to expand positional args and use ** to expand keyword args.
args = (1, 2, 3, 4)
kwargs = {"a": 3, "b": 4}
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
-# Function Scope
+# you can pass args and kwargs along to other functions that take args/kwargs
+# by expanding them with * and ** respectively
+def pass_all_the_args(*args, **kwargs):
+ all_the_args(*args, **kwargs)
+ print varargs(*args)
+ print keyword_args(**kwargs)
+
+# Function Scope
x = 5
def setX(num):
# Local var x not the same as global variable x
x = num # => 43
- print (x) # => 43
-
+ print x # => 43
+
def setGlobalX(num):
global x
- print (x) # => 5
+ print x # => 5
x = num # global var x is now set to 6
- print (x) # => 6
+ print x # => 6
setX(43)
setGlobalX(6)
@@ -430,11 +476,11 @@ 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]
+
####################################################
## 5. Classes
####################################################
-
# We subclass from object to get a class.
class Human(object):
@@ -467,10 +513,10 @@ class Human(object):
# Instantiate a class
i = Human(name="Ian")
-print(i.say("hi")) # prints out "Ian: hi"
+print i.say("hi") # prints out "Ian: hi"
j = Human("Joel")
-print(j.say("hello")) # prints out "Joel: hello"
+print j.say("hello") # prints out "Joel: hello"
# Call our class method
i.get_species() # => "H. sapiens"
@@ -490,12 +536,12 @@ Human.grunt() # => "*grunt*"
# You can import modules
import math
-print(math.sqrt(16)) # => 4
+print math.sqrt(16) # => 4
# You can get specific functions from a module
from math import ceil, floor
-print(ceil(3.7)) # => 4.0
-print(floor(3.7)) # => 3.0
+print ceil(3.7) # => 4.0
+print floor(3.7) # => 3.0
# You can import all functions from a module.
# Warning: this is not recommended
@@ -504,6 +550,9 @@ from math import *
# You can shorten module names
import math as m
math.sqrt(16) == m.sqrt(16) # => True
+# you can also test that the functions are equivalent
+from math import sqrt
+math.sqrt == m.sqrt == sqrt # => True
# Python modules are just ordinary python files. You
# can write your own, and import them. The name of the
@@ -530,14 +579,15 @@ def double_numbers(iterable):
# 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
+# 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)
+ print i
if i >= 30:
break
@@ -566,8 +616,8 @@ def say(say_please=False):
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 :(
+print say() # Can you buy me a beer?
+print say(say_please=True) # Can you buy me a beer? Please! I am poor :(
```
## Ready For More?