A for loop iterates over a sequence, so altering this sequence inside the loop could lead to unexpected results (especially when adding or removing elements):
alist = [0, 1, 2]
for index, value in enumerate(alist):
alist.pop(index)
print(alist)
# Out: [1]
Note: list.pop() is being used t...
You can define a new class using the class keyword.
class MyClass
end
Once defined, you can create a new instance using the .new method
somevar = MyClass.new
# => #<MyClass:0x007fe2b8aa4a18>
A class can have only one constructor, that is a method called initialize. The method is automatically invoked when a new instance of the class is created.
class Customer
def initialize(name)
@name = name.capitalize
end
end
sarah = Customer.new('sarah')
sarah.name #=> 'Sarah'
...
There are several special variable types that a class can use for more easily sharing data.
Instance variables, preceded by @. They are useful if you want to use the same variable in different methods.
class Person
def initialize(name, age)
my_age = age # local variable, will be destroyed ...
We have three methods:
attr_reader: used to allow reading the variable outside the class.
attr_writer: used to allow modifying the variable outside the class.
attr_accessor: combines both methods.
class Cat
attr_reader :age # you can read the age but you can never change it
attr_writer...
math.log(x) gives the natural (base e) logarithm of x.
math.log(math.e) # 1.0
math.log(1) # 0.0
math.log(100) # 4.605170185988092
math.log can lose precision with numbers close to 1, due to the limitations of floating-point numbers. In order to accurately calculate logs close to 1, ...
There is a problem when using optional arguments with a mutable default type (described in Defining a function with optional arguments), which can potentially lead to unexpected behaviour.
Explanation
This problem arises because a function's default arguments are initialised once, at the point whe...
Python 2.x2.3
raw_input will wait for the user to enter text and then return the result as a string.
foo = raw_input("Put a message here that asks the user for input")
In the above example foo will store whatever input the user provides.
Python 3.x3.0
input will wait for the user ...
Python 3.x3.0
In Python 3, print functionality is in the form of a function:
print("This string will be displayed in the output")
# This string will be displayed in the output
print("You can print \n escape characters too.")
# You can print escape characters too.
Pyth...
def input_number(msg, err_msg=None):
while True:
try:
return float(raw_input(msg))
except ValueError:
if err_msg is not None:
print(err_msg)
def input_number(msg, err_msg=None):
while True:
try:
return ...
Python 2.x2.3
In Python 2.x, to continue a line with print, end the print statement with a comma. It will automatically add a space.
print "Hello,",
print "World!"
# Hello, World!
Python 3.x3.0
In Python 3.x, the print function has an optional end parameter that is what...
The preferred method of file i/o is to use the with keyword. This will ensure the file handle is closed once the reading or writing has been completed.
with open('myfile.txt') as in_file:
content = in_file.read()
print(content)
or, to handle closing the file manually, you can forgo with...
with open('myfile.txt', 'w') as f:
f.write("Line 1")
f.write("Line 2")
f.write("Line 3")
f.write("Line 4")
If you open myfile.txt, you will see that its contents are:
Line 1Line 2Line 3Line 4
Python doesn't automatically add line b...
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(geolocationSuccess, geolocationFailure);
} else {
console.log("Geolocation is not supported by this browser.");
}
// Function that will be called if the query succeeds
var geolocationSuccess = function(pos) {...
In the event that geolocation fails, your callback function will receive a PositionError object. The object will include an attribute named code that will have a value of 1, 2, or 3. Each of these numbers signifies a different kind of error; the getErrorCode() function below takes the PositionError....
with open(input_file, 'r') as in_file, open(output_file, 'w') as out_file:
for line in in_file:
out_file.write(line)
Using the shutil module:
import shutil
shutil.copyfile(src, dst)
The following variables set up the below example:
var COOKIE_NAME = "Example Cookie"; /* The cookie's name. */
var COOKIE_VALUE = "Hello, world!"; /* The cookie's value. */
var COOKIE_PATH = "/foo/bar"; /* The cookie's path. */
var COOKIE_EXPIRES; ...
The following snippet encodes the data stored in d into JSON and stores it in a file (replace filename with the actual name of the file).
import json
d = {
'foo': 'bar',
'alice': 1,
'wonderland': [1, 2, 3]
}
with open(filename, 'w') as f:
json.dump(d, f)
