Considering goals automatically brings you to a consideration of contexts, or the situation/s in which you’re working toward your goals and your degree. Most students have at least three contexts in which they are pursuing a degree: personal, professional, and academic.
Personal Contexts
What, personally, has motivated you to pursue a degree at this point in time?
While the algorithms in this document do not perfectly isolate non-secure contexts from secure contexts (as discussed in § 5.1 Incomplete Isolation), the ancestor checks provide a fairly robust protection for the guarantees of authentication, confidentiality, and integrity that such contexts ought to provide. C) Everyday Life Philippine traditional art has always been a part of our daily lives.Its importance lies not only to its aesthetic appearance but also its function. Some artists deliberately foreground their cultural identity in their works. CONTENT Julie Lluch Travels, training. 3.3.1 Contexts explained When music is printed, many notational elements which do not appear explicitly in the input file must be added to the output. For example, compare the input and output of the following example. 1 The Pros and Cons of Working from Home 2 How To Study Effectively: 7 Simple Tips 3 7 Simple Rules to Live by to Get in Shape in Two Weeks 4 5 Practical Ways to Get Over a Mental Block 5 How to Learn Something New Every Day and Stay Smart. The Five Common Forms of Context Clues. Explanation Clues – These types of clues are dead give aways. They basically give you the definition in the same sentence or preceding sentence. Uninstaller sensei 1 3 1 – completely remove applications pdf. Organic food, which are foods that are produced without using common pesticides and chemicals, sells are starting to outpace standard foods in most.
- Do you want to complete a degree for personal fulfillment, perhaps completing something you started long ago, when the time was not right?
- Do you want to be an example for your children?
- Do you want to pursue a topic of personal interest?
Professional Contexts
If you intend to use your degree professionally, are you pursuing the degree because you
- notice that only co-workers with degrees are getting promotions?
- feel you need a degree in order to keep your current job?
- are interested in some particular aspect of your job and want to know more about it?
- want to change professions and/or move in a different direction within your current profession?
- are planning for a career in retirement?
Academic Contexts
What are your study interests?
- Do you want to pursue an associate or bachelor’s degree?
- Do you have a particular academic field of interest?
- Is your academic interest related to a personal or professional goal?
- If you had the luxury of not being pragmatic about pursuing a degree and could study anything at all, what would it be?
Articulating the contexts in which you’re pursuing a degree may help you make decisions about the contents and focus of your degree.
The choices you make for your degree depend on the context as well as your goals. You could make very different course choices depending on personal, professional, and/or academic contexts. Consider all relevant contexts, and consider how these contexts might impact your choices.
Compound statements contain (groups of) other statements; they affect or controlthe execution of those other statements in some way. In general, compoundstatements span multiple lines, although in simple incarnations a whole compoundstatement may be contained in one line.
The
if
, while
and for
statements implementtraditional control flow constructs. try
specifies exceptionhandlers and/or cleanup code for a group of statements, while thewith
statement allows the execution of initialization andfinalization code around a block of code. Function and class definitions arealso syntactically compound statements.A compound statement consists of one or more ‘clauses.’ A clause consists of aheader and a ‘suite.’ The clause headers of a particular compound statement areall at the same indentation level. Each clause header begins with a uniquelyidentifying keyword and ends with a colon. A suite is a group of statementscontrolled by a clause. A suite can be one or more semicolon-separated simplestatements on the same line as the header, following the header’s colon, or itcan be one or more indented statements on subsequent lines. Only the latterform of a suite can contain nested compound statements; the following is illegal,mostly because it wouldn’t be clear to which
if
clause a followingelse
clause would belong:Also note that the semicolon binds tighter than the colon in this context, sothat in the following example, either all or none of the
print()
calls areexecuted:Summarizing:
Note that statements always end in a
NEWLINE
possibly followed by aDEDENT
. Also note that optional continuation clauses always begin with akeyword that cannot start a statement, thus there are no ambiguities (the‘dangling else
’ problem is solved in Python by requiring nestedif
statements to be indented).The formatting of the grammar rules in the following sections places each clauseon a separate line for clarity.
8.1. The if
statement¶
The
if
statement is used for conditional execution:It selects exactly one of the suites by evaluating the expressions one by oneuntil one is found to be true (see section Boolean operations for the definition oftrue and false); then that suite is executed (and no other part of the
if
statement is executed or evaluated). If all expressions arefalse, the suite of the else
clause, if present, is executed.8.2. The while
statement¶
The
while
statement is used for repeated execution as long as anexpression is true:This repeatedly tests the expression and, if it is true, executes the firstsuite; if the expression is false (which may be the first time it is tested) thesuite of the
else
clause, if present, is executed and the loopterminates.A
break
statement executed in the first suite terminates the loopwithout executing the else
clause’s suite. A continue
statement executed in the first suite skips the rest of the suite and goes backto testing the expression.8.3. The for
statement¶
The
for
statement is used to iterate over the elements of a sequence(such as a string, tuple or list) or other iterable object:The expression list is evaluated once; it should yield an iterable object. Aniterator is created for the result of the
expression_list
. The suite isthen executed once for each item provided by the iterator, in the order returnedby the iterator. Each item in turn is assigned to the target list using thestandard rules for assignments (see Assignment statements), and then the suite isexecuted. When the items are exhausted (which is immediately when the sequenceis empty or an iterator raises a StopIteration
exception), the suite inthe else
clause, if present, is executed, and the loop terminates.A
break
statement executed in the first suite terminates the loopwithout executing the else
clause’s suite. A continue
statement executed in the first suite skips the rest of the suite and continueswith the next item, or with the else
clause if there is no nextitem.The for-loop makes assignments to the variables in the target list.This overwrites all previous assignments to those variables includingthose made in the suite of the for-loop:
Names in the target list are not deleted when the loop is finished, but if thesequence is empty, they will not have been assigned to at all by the loop. Hint:the built-in function
range()
returns an iterator of integers suitable toemulate the effect of Pascal’s fori:=atobdo
; e.g., list(range(3))
returns the list [0,1,2]
.Note
There is a subtlety when the sequence is being modified by the loop (this canonly occur for mutable sequences, e.g. lists). An internal counter is usedto keep track of which item is used next, and this is incremented on eachiteration. When this counter has reached the length of the sequence the loopterminates. This means that if the suite deletes the current (or a previous)item from the sequence, the next item will be skipped (since it gets theindex of the current item which has already been treated). Likewise, if thesuite inserts an item in the sequence before the current item, the currentitem will be treated again the next time through the loop. This can lead tonasty bugs that can be avoided by making a temporary copy using a slice ofthe whole sequence, e.g.,
8.4. The try
statement¶
The
try
statement specifies exception handlers and/or cleanup codefor a group of statements:The
except
clause(s) specify one or more exception handlers. When noexception occurs in the try
clause, no exception handler is executed.When an exception occurs in the try
suite, a search for an exceptionhandler is started. This search inspects the except clauses in turn until oneis found that matches the exception. An expression-less except clause, ifpresent, must be last; it matches any exception. For an except clause with anexpression, that expression is evaluated, and the clause matches the exceptionif the resulting object is “compatible” with the exception. An object iscompatible with an exception if it is the class or a base class of the exceptionobject or a tuple containing an item compatible with the exception.If no except clause matches the exception, the search for an exception handlercontinues in the surrounding code and on the invocation stack. 1
If the evaluation of an expression in the header of an except clause raises anexception, the original search for a handler is canceled and a search starts forthe new exception in the surrounding code and on the call stack (it is treatedas if the entire
try
statement raised the exception).When a matching except clause is found, the exception is assigned to the targetspecified after the
as
keyword in that except clause, if present, andthe except clause’s suite is executed. All except clauses must have anexecutable block. When the end of this block is reached, execution continuesnormally after the entire try statement. (This means that if two nestedhandlers exist for the same exception, and the exception occurs in the tryclause of the inner handler, the outer handler will not handle the exception.)When an exception has been assigned using
astarget
, it is cleared at theend of the except clause. This is as ifwas translated to
This means the exception must be assigned to a different name to be able torefer to it after the except clause. Exceptions are cleared because with thetraceback attached to them, they form a reference cycle with the stack frame,keeping all locals in that frame alive until the next garbage collection occurs.
Before an except clause’s suite is executed, details about the exception arestored in the
sys
module and can be accessed via sys.exc_info()
.sys.exc_info()
returns a 3-tuple consisting of the exception class, theexception instance and a traceback object (see section The standard type hierarchy) identifyingthe point in the program where the exception occurred. sys.exc_info()
values are restored to their previous values (before the call) when returningfrom a function that handled an exception.The optional
else
clause is executed if the control flow leaves thetry
suite, no exception was raised, and no return
,continue
, or break
statement was executed. Exceptions inthe else
clause are not handled by the preceding except
clauses.If
finally
is present, it specifies a ‘cleanup’ handler. Thetry
clause is executed, including any except
andelse
clauses. If an exception occurs in any of the clauses and isnot handled, the exception is temporarily saved. The finally
clauseis executed. If there is a saved exception it is re-raised at the end of thefinally
clause. If the finally
clause raises anotherexception, the saved exception is set as the context of the new exception.If the finally
clause executes a return
, break
or continue
statement, the saved exception is discarded:The exception information is not available to the program during execution ofthe
finally
clause.When a
return
, break
or continue
statement isexecuted in the try
suite of a try
…finally
statement, the finally
clause is also executed ‘on the way out.’The return value of a function is determined by the last
return
statement executed. Since the finally
clause always executes, areturn
statement executed in the finally
clause willalways be the last one executed:Additional information on exceptions can be found in section Exceptions,and information on using the
raise
statement to generate exceptionsmay be found in section The raise statement.Changed in version 3.8: Prior to Python 3.8, a
continue
statement was illegal in thefinally
clause due to a problem with the implementation.8.5. The with
statement¶
The
with
statement is used to wrap the execution of a block withmethods defined by a context manager (see section With Statement Context Managers).This allows common try
…except
…finally
usage patterns to be encapsulated for convenient reuse.The execution of the
with
statement with one “item” proceeds as follows:- The context expression (the expression given in the
with_item
) isevaluated to obtain a context manager. - The context manager’s
__enter__()
is loaded for later use. - The context manager’s
__exit__()
is loaded for later use. - The context manager’s
__enter__()
method is invoked. - If a target was included in the
with
statement, the return valuefrom__enter__()
is assigned to it.NoteThewith
statement guarantees that if the__enter__()
method returns without an error, then__exit__()
will always becalled. Thus, if an error occurs during the assignment to the target list,it will be treated the same as an error occurring within the suite wouldbe. See step 6 below. - The suite is executed.
- The context manager’s
__exit__()
method is invoked. If an exceptioncaused the suite to be exited, its type, value, and traceback are passed asarguments to__exit__()
. Otherwise, threeNone
arguments aresupplied.If the suite was exited due to an exception, and the return value from the__exit__()
method was false, the exception is reraised. If the returnvalue was true, the exception is suppressed, and execution continues with thestatement following thewith
statement.If the suite was exited for any reason other than an exception, the returnvalue from__exit__()
is ignored, and execution proceeds at the normallocation for the kind of exit that was taken.
The following code:
is semantically equivalent to:
With more than one item, the context managers are processed as if multiple
with
statements were nested:is semantically equivalent to:
Changed in version 3.1: Support for multiple context expressions.
See also
The specification, background, and examples for the Python
with
statement.8.6. Function definitions¶
A function definition defines a user-defined function object (see sectionThe standard type hierarchy):
A function definition is an executable statement. Its execution binds thefunction name in the current local namespace to a function object (a wrapperaround the executable code for the function). This function object contains areference to the current global namespace as the global namespace to be usedwhen the function is called.
The function definition does not execute the function body; this gets executedonly when the function is called. 2
A function definition may be wrapped by one or more decorator expressions.Decorator expressions are evaluated when the function is defined, in the scopethat contains the function definition. The result must be a callable, which isinvoked with the function object as the only argument. The returned value isbound to the function name instead of the function object. Multiple decoratorsare applied in nested fashion. For example, the following code
is roughly equivalent to
except that the original function is not temporarily bound to the name
func
.Changed in version 3.9: Functions may be decorated with any valid
assignment_expression
.Previously, the grammar was much more restrictive; see PEP 614 fordetails.When one or more parameters have the form parameter
=
expression, the function is said to have “default parameter values.” For aparameter with a default value, the corresponding argument may beomitted from a call, in whichcase the parameter’s default value is substituted. If a parameter has a defaultvalue, all following parameters up until the “*
” must also have a defaultvalue — this is a syntactic restriction that is not expressed by the grammar.Default parameter values are evaluated from left to right when the functiondefinition is executed. This means that the expression is evaluated once, whenthe function is defined, and that the same “pre-computed” value is used for eachcall. This is especially important to understand when a default parameter is amutable object, such as a list or a dictionary: if the function modifies theobject (e.g. by appending an item to a list), the default value is in effectmodified. This is generally not what was intended. A way around this is to use
None
as the default, and explicitly test for it in the body of the function,e.g.:Function call semantics are described in more detail in section Calls. Afunction call always assigns values to all parameters mentioned in the parameterlist, either from position arguments, from keyword arguments, or from defaultvalues. If the form “
*identifier
” is present, it is initialized to a tuplereceiving any excess positional parameters, defaulting to the empty tuple.If the form “**identifier
” is present, it is initialized to a newordered mapping receiving any excess keyword arguments, defaulting to anew empty mapping of the same type. Parameters after “*
” or“*identifier
” are keyword-only parameters and may only be passedused keyword arguments.Parameters may have an annotation of the form “
:expression
”following the parameter name. Any parameter may have an annotation, even those of the form*identifier
or **identifier
. Functions may have “return” annotation ofthe form “->expression
” after the parameter list. These annotations can beany valid Python expression. The presence of annotations does not change thesemantics of a function. The annotation values are available as values ofa dictionary keyed by the parameters’ names in the __annotations__
attribute of the function object. If the annotations
import from__future__
is used, annotations are preserved as strings at runtime whichenables postponed evaluation. Otherwise, they are evaluated when the functiondefinition is executed. In this case annotations may be evaluated ina different order than they appear in the source code.It is also possible to create anonymous functions (functions not bound to aname), for immediate use in expressions. This uses lambda expressions, described insection Lambdas. Note that the lambda expression is merely a shorthand for asimplified function definition; a function defined in a “
def
”statement can be passed around or assigned to another name just like a functiondefined by a lambda expression. The “def
” form is actually more powerfulsince it allows the execution of multiple statements and annotations.Programmer’s note: Functions are first-class objects. A “
def
” statementexecuted inside a function definition defines a local function that can bereturned or passed around. Free variables used in the nested function canaccess the local variables of the function containing the def. See sectionNaming and binding for details.See also
The original specification for function annotations.
Definition of a standard meaning for annotations: type hints.
Ability to type hint variable declarations, including classvariables and instance variables
Support for forward references within annotations by preservingannotations in a string form at runtime instead of eager evaluation.
8.7. Class definitions¶
A class definition defines a class object (see section The standard type hierarchy):
A class definition is an executable statement. The inheritance list usuallygives a list of base classes (see Metaclasses for more advanced uses), soeach item in the list should evaluate to a class object which allowssubclassing. Classes without an inheritance list inherit, by default, from thebase class
object
; hence,is equivalent to
The class’s suite is then executed in a new execution frame (see Naming and binding),using a newly created local namespace and the original global namespace.(Usually, the suite contains mostly function definitions.) When the class’ssuite finishes execution, its execution frame is discarded but its localnamespace is saved. 3 A class object is then created using the inheritancelist for the base classes and the saved local namespace for the attributedictionary. The class name is bound to this class object in the original localnamespace.
The order in which attributes are defined in the class body is preservedin the new class’s
__dict__
. Note that this is reliable only rightafter the class is created and only for classes that were defined usingthe definition syntax.Class creation can be customized heavily using metaclasses.
Classes can also be decorated: just like when decorating functions,
is roughly equivalent to
The evaluation rules for the decorator expressions are the same as for functiondecorators. The result is then bound to the class name.
Changed in version 3.9: Classes may be decorated with any valid
assignment_expression
.Previously, the grammar was much more restrictive; see PEP 614 fordetails.Programmer’s note: Variables defined in the class definition are classattributes; they are shared by instances. Instance attributes can be set in amethod with
self.name=value
. Both class and instance attributes areaccessible through the notation “self.name
”, and an instance attribute hidesa class attribute with the same name when accessed in this way. Classattributes can be used as defaults for instance attributes, but using mutablevalues there can lead to unexpected results. Descriptorscan be used to create instance variables with different implementation details.![Contexts Contexts](https://media.cheggcdn.com/media/9bc/9bc1ed5f-08cc-432a-80e4-a252a3ce3b78/phpCTanqI.png)
See also
The proposal that changed the declaration of metaclasses to the currentsyntax, and the semantics for how classes with metaclasses areconstructed.
The proposal that added class decorators. Function and method decoratorswere introduced in PEP 318.
8.8. Coroutines¶
8.8.1. Coroutine function definition¶
Execution of Python coroutines can be suspended and resumed at many points(see coroutine). Inside the body of a coroutine function,
await
andasync
identifiers become reserved keywords; await
expressions,asyncfor
and asyncwith
can only be used incoroutine function bodies.Functions defined with
asyncdef
syntax are always coroutine functions,even if they do not contain await
or async
keywords.It is a
SyntaxError
to use a yieldfrom
expression inside the bodyof a coroutine function.An example of a coroutine function:
8.8.2. The asyncfor
statement¶
An asynchronous iterable is able to call asynchronous code in itsiter implementation, and asynchronous iterator can call asynchronouscode in its next method.
The
asyncfor
statement allows convenient iteration over asynchronousiterators.The following code:
Is semantically equivalent to:
See also
__aiter__()
and __anext__()
for details.It is a
SyntaxError
to use an asyncfor
statement outside thebody of a coroutine function.Contexts 3 7 11
8.8.3. The asyncwith
statement¶
An asynchronous context manager is a context manager that isable to suspend execution in its enter and exit methods.
The following code:
is semantically equivalent to:
See also
__aenter__()
and __aexit__()
for details.It is a
SyntaxError
to use an asyncwith
statement outside thebody of a coroutine function.See also
The proposal that made coroutines a proper standalone concept in Python,and added supporting syntax.
Footnotes
The exception is propagated to the invocation stack unlessthere is a
finally
clause which happens to raise anotherexception. That new exception causes the old one to be lost.A string literal appearing as the first statement in the function body istransformed into the function’s
__doc__
attribute and therefore thefunction’s docstring.Contexts 3 7 14
A string literal appearing as the first statement in the class body istransformed into the namespace’s
__doc__
item and therefore the class’sdocstring.