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Diffstat (limited to 'python.html.markdown')
| -rw-r--r-- | python.html.markdown | 161 |
1 files changed, 125 insertions, 36 deletions
diff --git a/python.html.markdown b/python.html.markdown index 63547bf6..675967f4 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -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 reachong end of life and will stop beeign maintained in 2020, +it is though recommended to start learnign 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 @@ -46,12 +53,18 @@ to Python 2.x. For Python 3.x, take a look at the [Python 3 tutorial](http://lea 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 -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 @@ -141,12 +154,14 @@ bool("") # => False ## 2. Variables and Collections #################################################### -# Python has a print statement, in all 2.x versions but removed from 3. -print "I'm Python. Nice to meet you!" -# Python also has a print function, available in versions 2.7 and 3... -# but for 2.7 you need to add the import (uncommented): -# from __future__ import print_function -print("I'm also Python! ") +# 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 @@ -157,6 +172,7 @@ 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 @@ -195,7 +211,7 @@ 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] @@ -210,6 +226,17 @@ 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) # => 3 +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 @@ -301,6 +328,15 @@ 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 @@ -316,11 +352,11 @@ 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." """ @@ -331,8 +367,8 @@ prints: mouse is a mammal """ for animal in ["dog", "cat", "mouse"]: - # You can use % to interpolate formatted strings - print("%s is a mammal" % animal) + # You can use {0} to interpolate formatted strings. (See above.) + print "{0} is a mammal".format(animal) """ "range(number)" returns a list of numbers @@ -344,7 +380,19 @@ 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. @@ -356,7 +404,7 @@ prints: """ x = 0 while x < 4: - print(x) + print x x += 1 # Shorthand for x = x + 1 # Handle exceptions with a try/except block @@ -371,7 +419,13 @@ except (TypeError, NameError): pass # Multiple exceptions can be handled together, if required. else: # Optional clause to the try/except block. Must follow all except blocks print "All good!" # Runs only if the code in try raises no exceptions +finally: # Execute under all circumstances + print "We can clean up resources here" +# Instead of try/finally to cleanup resources you can use a with statement +with open("myfile.txt") as f: + for line in f: + print line #################################################### ## 4. Functions @@ -379,7 +433,7 @@ 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 {0} and y is {1}".format(x, y) return x + y # Return values with a return statement # Calling functions with parameters @@ -398,7 +452,7 @@ 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 map if you do not use ** +# keyword args, as well, which will be interpreted as a dict if you do not use ** def keyword_args(**kwargs): return kwargs @@ -408,8 +462,8 @@ 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) @@ -431,22 +485,22 @@ def pass_all_the_args(*args, **kwargs): print varargs(*args) print keyword_args(**kwargs) -# Function Scope +# 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): @@ -459,9 +513,12 @@ 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 @@ -487,9 +544,13 @@ 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 "%s: %s" % (self.name, msg) + return "{0}: {1}".format(self.name, msg) # A class method is shared among all instances # They are called with the calling class as the first argument @@ -502,13 +563,30 @@ 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") -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" @@ -521,6 +599,16 @@ 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 @@ -528,12 +616,12 @@ 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 @@ -579,7 +667,7 @@ 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 @@ -608,24 +696,25 @@ 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? ### Free Online +* [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/) * [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/) ### Dead Tree * [Programming Python](http://www.amazon.com/gp/product/0596158106/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596158106&linkCode=as2&tag=homebits04-20) * [Dive Into Python](http://www.amazon.com/gp/product/1441413022/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1441413022&linkCode=as2&tag=homebits04-20) * [Python Essential Reference](http://www.amazon.com/gp/product/0672329786/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0672329786&linkCode=as2&tag=homebits04-20) - |