on 31-Jan-2017 (Tue)

Every value in Python has a class that determines what type of value it is.

Values that share a class also share behavior.

The built-in type function allows us to inspect the class of any value

The values we have used so far are instances of a small number of native data types that are built into the Python language. Native data types have the following properties:

1. There are expressions that evaluate to values of native types, called literals.
2. There are built-in functions and operators to manipulate values of native types.

The int class is the native data type used to represent integers. Integer literals (sequences of adjacent numerals) evaluate to int values, and mathematical operators manipulate these values.

Python includes three native numeric types: integers ( int ), real numbers ( float ), and complex numbers ( complex ).

int objects represent integers exactly, without any approximation or limits on their size. On the other hand, float objects can represent a wide range of fractional numbers, but not all numbers can be represented exactly, and there are minimum and maximum values. Therefore, float values should be treated as approximations to real values.

Although int values are combined above, dividing one int by another yields a float value: a truncated finite approximation to the actual ratio of the two integers divided.

 >>> type ( 1 / 3 ) <class 'float'> >>> 1 / 3 0.3333333333333333 

Problems with this approximation appear when we conduct equality tests.

 >>> 1 / 3 == 0.333333333333333312345 # Beware of float approximation True 

The general technique of isolating the parts of a program that deal with how data are represented from the parts that deal with how data are manipulated is a powerful design methodology called data abstraction. Data abstraction makes programs much easier to design, maintain, and modify.

data abstraction isolates how a compound data value is used from the details of how it is constructed.

The basic idea of data abstraction is to structure programs so that they operate on abstract data. That is, our programs should use data in such a way as to make as few assumptions about the data as possible. At the same time, a concrete data representation is defined as an independent part of the program.

We are using here a powerful strategy for designing programs: wishful thinking. We haven't yet said how a rational number is represented, or how the functions numer , denom , and rational should be implemented. Even so, if we did define these three functions, we could then add, multiply, print, and test equality of rational numbers:

a list , which can be constructed by placing expressions within square brackets separated by commas. Such an expression is called a list literal.

The elements of a list can be accessed in two ways. The first way is via our familiar method of multiple assignment, which unpacks a list into its elements and binds each element to a different name.

One intuition that supports this indexing convention is that the index represents how far an element is offset from the beginning of the list.

The equivalent function for the element selection operator is called getitem , and it also uses 0-indexed positions to select elements from a list.

The floor division operator, // , expresses integer division, which rounds down the fractional part of the result of division.

In general, the underlying idea of data abstraction is to identify a basic set of operations in terms of which all manipulations of values of some kind will be expressed, and then to use only those operations in manipulating the data. By restricting the use of operations in this way, it is much easier to change the representation of abstract data without changing the behavior of a program.

An abstraction barrier violation occurs whenever a part of the program that can use a higher level function instead uses a function in a lower level.

Abstraction barriers make programs easier to maintain and to modify. The fewer functions that depend on a particular representation, the fewer changes are required when one wants to change that representation.

In general, we can express abstract data using a collection of selectors and constructors, together with some behavior conditions. As long as the behavior conditions are met (such as the division property above), the selectors and constructors constitute a valid representation of a kind of data. The implementation details below an abstraction barrier may change, but if the behavior does not, then the data abstraction remains valid, and any program written using this data abstraction will remain correct.

The behavior we require to implement a pair is that it glues two values together. Stated as a behavior condition,

• If a pair p was constructed from values x and y , then select(p, 0) returns x , and select(p, 1) returns y .

Functions are sufficient to represent compound data.

A sequence is an ordered collection of values

Sequences are not instances of a particular built-in type or abstract data representation, but instead a collection of behaviors that are shared among several different types of data.

there are many kinds of sequences, but they all share common behavior. In particular,

Length. A sequence has a finite length. An empty sequence has length 0.

Element selection. A sequence has an element corresponding to any non-negative integer index less than its length, starting at 0 for the first element.

A list value is a sequence that can have arbitrary length.

which evaluates to a list instance, as well as an element selection expression that evaluates to a value in the list.

lists can be added together and multiplied by integers. For sequences, addition and multiplication do not add or multiply elements, but instead combine and replicate the sequences themselves. That is, the add function in the operator module (and the + operator) yields a list that is the concatenation of the added arguments. The mul function in operator (and the * operator) can take a list and an integer k to return the list that consists of k repetitions of the original list.

A for statement is executed by the following procedure:

1. Evaluate the header <expression> , which must yield an iterable value.
2. For each element value in that iterable value, in order:
   1. Bind <name> to that value in the current frame.
   2. Execute the <suite> .

This execution procedure refers to iterable values. Lists are a type of sequence, and sequences are iterable values. Their elements are considered in their sequential order.

An important consequence of this evaluation procedure is that <name> will be bound to the last element of the sequence after the for statement is executed. The for loop introduces yet another way in which the environment can be updated by a statement.

A common pattern in programs is to have a sequence of elements that are themselves sequences, but all of a fixed length. A for statement may include multiple names in its header to "unpack" each element sequence into its respective elements.

This pattern of binding multiple names to multiple values in a fixed-length sequence is called sequence unpacking; it is the same pattern that we see in assignment statements that bind multiple names to multiple values.

A range is another built-in type of sequence in Python, which represents a range of integers.

Calling the list constructor on a range evaluates to a list with the same elements as the range, so that the elements can be easily inspected.

If only one argument is given, it is interpreted as one beyond the last value for a range that starts at 0.

 >>> list ( range ( 4 )) [0, 1, 2, 3] 

Ranges commonly appear as the expression in a for header to specify the number of times that the suite should be executed: A common convention is to use a single underscore character for the name in the for header if the name is unused in the suite:

Modular components that have sequences as both inputs and outputs can be mixed and matched to perform data processing. Complex components can be defined by chaining together a pipeline of sequence processing operations, each of which is simple and focused.

Many sequence processing operations can be expressed by evaluating a fixed expression for each element in a sequence and collecting the resulting values in a result sequence. In Python, a list comprehension is an expression that performs such a computation.

Another common sequence processing operation is to select a subset of values that satisfy some condition. List comprehensions can also express this pattern, for instance selecting all elements of odds that evenly divide 25 .

 >>> [ x for x in odds if 25 % x == 0 ] [1, 5] 

The general form of a list comprehension is:

[<map expression> for <name> in <sequence expression> if <filter expression>]

To evaluate a list comprehension, Python evaluates the <sequence expression> , which must return an iterable value. Then, for each element in order, the element value is bound to <name> , the filter expression is evaluated, and if it yields a true value, the map expression is evaluated. The values of the map expression are collected into a list.

A third common pattern in sequence processing is to aggregate all values in a sequence into a single value. The built-in functions sum , min , and max are all examples of aggregation functions.

In the computer science community, the more common name for apply_to_all is map and the more common name for keep_if is filter . In Python, the built-in map and filter are generalizations of these functions that do not return lists

In Python programs, it is more common to use list comprehensions directly rather than higher-order functions, but both approaches to sequence processing are widely used.

A value can be tested for membership in a sequence. Python has two operators in and not in that evaluate to True or False depending on whether an element appears in a sequence.

Sequences contain smaller sequences within them. A slice of a sequence is any contiguous span of the original sequence, designated by a pair of integers. As with the range constructor, the first integer indicates the starting index of the slice and the second indicates one beyond the ending index.

In Python, sequence slicing is expressed similarly to element selection, using square brackets. A colon separates the starting and ending indices. Any bound that is omitted is assumed to be an extreme value: 0 for the starting index, and the length of the sequence for the ending index.

Slicing can be used on the branches of a tree as well. For example, we may want to place a restriction on the number of branches in a tree. A binary tree is either a leaf or a sequence of at most two binary trees. A common tree transformation called binarization computes a binary tree from an original tree by grouping together adjacent branches.

The native data type for text in Python is called a string, and corresponds to the constructor str .

String literals can express arbitrary text, surrounded by either single or double quotation marks.

Strings satisfy the two basic conditions of a sequence that we introduced at the beginning of this section: they have a length and they support element selection.

The elements of a string are themselves strings that have only a single character. A character is any single letter of the alphabet, punctuation mark, or other symbol. Unlike many other programming languages, Python does not have a separate character type; any text is a string, and strings that represent single characters have a length of 1.

Like lists, strings can also be combined via addition and multiplication.

 >>> 'Berkeley' + ', CA' 'Berkeley, CA' >>> 'Shabu ' * 2 'Shabu Shabu ' 

The behavior of strings diverges from other sequence types in Python. The string abstraction does not conform to the full sequence abstraction that we described for lists and ranges. In particular, the membership operator in applies to strings, but has an entirely different behavior than when it is applied to sequences. It matches substrings rather than elements.

String Coercion. A string can be created from any object in Python by calling the str constructor function with an object value as its argument. This feature of strings is useful for constructing descriptive strings from objects of various types.

Our ability to use lists as the elements of other lists provides a new means of combination in our programming language. This ability is called a closure property of a data type.

a method for combining data values has a closure property if the result of combination can itself be combined using the same method. Closure is the key to power in any means of combination because it permits us to create hierarchical structures — structures made up of parts, which themselves are made up of parts, and so on.

We can visualize lists in environment diagrams using box-and-pointer notation. A list is depicted as adjacent boxes that contain the elements of the list. Primitive values such as numbers, strings, boolean values, and None appear within an element box. Composite values, such as function values and other lists, are indicated by an arrow.

The tree is a fundamental data abstraction that imposes regularity on how hierarchical values are structured and manipulated.

A tree has a root value and a sequence of branches. Each branch of a tree is a tree. A tree with no branches is called a leaf. Any tree contained within a tree is called a sub-tree of that tree (such as a branch of a branch). The root value of a sub-tree of a tree is called a node (or node value) in that tree.

Trees can be constructed by nested expressions.

Partition trees. Trees can also be used to represent the partitions of an integer. A partition tree for n using parts up to size m is a binary (two branch) tree that represents the choices taken during computation. In a non-leaf partition tree:

• the left (index 0) branch contains all ways of partitioning n using at least one m ,
• the right (index 1) branch contains partitions using parts up to m-1 , and
• the root value is m .

The values at the leaves of a partition tree express whether the path from the root of the tree to the leaf represents a successful partition of n .

A linked list is a pair containing the first element of the sequence (in this case 1) and the rest of the sequence (in this case a representation of 2, 3, 4). The second element is also a linked list. The rest of the inner-most linked list containing only 4 is 'empty' , a value that represents an empty linked list.

Linked lists have recursive structure: the rest of a linked list is a linked list or 'empty' . We can define an abstract data representation to validate, construct, and select the components of linked lists.

The behavior condition for a linked list is that, like a pair, its constructor and selectors are inverse functions.

• If a linked list s was constructed from first element f and linked list r , then first(s) returns f , and rest(s) returns r .

a common pattern of computation with linked lists, where each step in an iteration operates on an increasingly shorter suffix of the original list. This incremental processing to find the length and elements of a linked list does take some time to compute. Python's built-in sequence types are implemented in a different way that does not have a large cost for computing the length of a sequence or retrieving its elements.

Linked lists are particularly useful when constructing sequences incrementally, a situation that arises often in recursive computations.

We follow the same recursive analysis of the problem as we did while counting: partitioning n using integers up to m involves either

1. partitioning n-m using integers up to m , or
2. partitioning n using integers up to m-1 .

For base cases, we find that 0 has an empty partition, while partitioning a negative integer or using parts smaller than 1 is impossible.

Interrupt to show you are really excited about what they are saying.

Masters always want to feel secure in their positions, and superior to those around them in intelligence, wit, and charm.

If you have to entertaining your master, display limited means to win his sympathy.

A man of power, often has dirty work that has to be done, but for the sake of appearances it is generally preferable to have other people do it for him; friends often do this the best, since their affection for him makes them willing to take chances.

The key to this technique is to agree with the critique or joke. Understand that what this person is really doing is that they are just letting you recognize your flaws.

When somebody asks for your advice you ar in a great position to influence them.

Just convince them to go the direction you want.

Any attempt to influence someone in any direction will be instantly more powerful and effective if the person being influenced perceives the person influencing to be of higher authority.

When you start using numbers, saying there is only this much tie or this many days, or this many of it left. Then it gets really powerful.

How can you develop an urge to get better at dealing with people? By constantly reminding yourself how important these principles are to you.

Bernard Shaw once remarked: “If you teach a man anything, he will never learn.” Shaw was right. Learning is an active process. We learn by doing.

“IF YOU WANT TO GATHER HONEY, DON’T KICK OVER THE BEEHIVE”

Nobody, doesnt matter how bad they are, blame theirselves for anything.

If Al Capone, “Two Gun” Crowley, Dutch Schultz, and the desperate men and women behind prison walls don’t blame themselves for anything , what about the people with whom you and I come in contact?

I personally had to blunder through this old world for a third of a century before it even began to dawn upon me that ninety- nine times out of a hundred, people don’t criticize themselves for anything, no matter how wrong it may be.

Criticism is futile because it puts a person on the defensive and usually makes them strive to justify themselves. Criticism is dangerous, because it wounds a person’s precious pride, hurts their sense of importance, and arouses resentment

It is proven that an animal rewarded for good behavior will learn much more rapidly and retain what it learns far more effectively than an animal punished for bad behavior.

As much as we thirst for approval, we dread condemnation,”

one safety coordinator dude trying to make people put on their hardhat.

First: He reported that whenever he came across workers not wearing hard hats, he would tell them with a lot of authority of the regulation and that they must comply.
Result:They puted it on, and after he left, they removed the hats.

Experiment: The next time he found some of the workers not wearing their hard hat, he asked if the hats were uncomfortable or did not fit properly. Then he reminded the men that the hat was designed to protect them and suggested that it always be worn on the job.

Result: increased compliance with no resentment or emotional upset.

People do not necessarily know where their emotions are coming from. You can lead their emotions, in many man ways.

When you keep referring to that high point but with different reference points and different approaches, you are reawakening the emotional urgency the person you're talking to has in your conversation.

Capital expenditure, or CapEx, are funds used by a company to acquire or upgrade physical assets such as property, industrial buildings or equipment.

Capex is often used to undertake new projects or investments by the firm.

Capex can include everything from repairing a roof to building, to purchasing a piece of equipment, or building a brand new factory.

In terms of accounting, an expense is considered to be a capital expenditure when the asset is a newly purchased capital asset or an investment that improves the useful life of an existing capital asset.

If an expense is a capital expenditure, it needs to be capitalized. This requires the company to spread the cost of the expenditure (the fixed cost) over the useful life of the asset.

Capital expenditure should not be confused with revenue expenditure or operating expenses (OPEX). Revenue expenses are shorter-term expenses required to meet the ongoing operational costs of running a business, and therefore they are essentially identical to operating expenses.

Unlike capital expenditures, revenue expenses can be fully tax-deducted in the same year in which the expenses occur.

Mnemonic Link System or just MLS links dobes together into a story. (IM-based) MLS is the most often used linking technique. * MLS and IM form traditional linking techniques *

Pinned Link System (PLS) is a special and stronger case of MLS. It picks some additional bases and creates links between them and some dobes of the chain.

Yes, we were friends before, but our friendship was based on what power we had.... I was friends with you, good brahman, because it served my purpose. No pauper is friend to the rich, no fool to the wise, no coward to the brave. An old friend—who needs him? It is two men of equal wealth and equal birth who contract friendship and marriage, not a rich man and a pauper.... An old friend—who needs him?

If you never expect gratitude from a friend, you will be pleasantly surprised when they do prove grateful.

An enemy at our heels sharpens our wits, keeping us focused and alert. It is sometimes better, then, to use enemies as enemies rather than transforming them into friends or allies.

This scapegoat “fall of the favorite” was a trick often used by kings and sovereigns: They would let their closest friend at court take the fall for a mistake, since the public would not believe that they would deliberately sacrifice a friend for such a purpose.

This principle also comes across in the weight we give the advice of other people around us – even people unqualified to give a good opinion.

So if an office goer is unsure of what he should wear to a meeting, then he is sure to consult a colleague and wear a similar outfit.

If a child is unsure of which ice cream flavor to pick, then she is sure to consult a friend or sibling to choose a flavor.

In action, you can influence people to act the way you want them to act by getting them to agree and say ‘yes’ and take very small actions in the direction you want them to go in.