Urwid 0.9.8.1 Tutorial
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1. Hello World Example
2. Conversation Example
3. Zen of ListBox
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4. Combining Widgets
5. Creating Custom Widgets
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1. Hello World Example
This program displays the string "Hello World" in the top left corner
of the screen and waits for a keypress before exiting.
import urwid.curses_display
import urwid
ui = urwid.curses_display.Screen()
def run():
canvas = urwid.TextCanvas(["Hello World"])
ui.draw_screen( (20, 1), canvas )
while not ui.get_input():
pass
ui.run_wrapper( run )
- The curses_display.Screen
class provides access to the curses library. Its member function
run_wrapper initializes
curses full-screen mode and then calls the "run" function passed. It will
also take care of restoring the screen when the "run" function exits.
- A TextCanvas is created
containing one row with the string "Hello World".
- The canvas is passed to the
draw_screen function along
with a fixed screen size of 20 columns and 1 row. If the
terminal window this program is run from is larger than 20 by 1 the
text will appear in the top left corner.
- The get_input function
is then called until it returns something. It must be called in a loop
because by default it will time out after one second and return an
empty list when there is no input.
Creating canvases directly in this way is generally only done when
writing custom widget classes. Note that the draw_screen
function must be passed a canvas and a screen size that matches it,
for backwards compatibility.
This program displays the string "Hello World" in the center of the screen
and waits for a keypress before exiting.
import urwid.curses_display
import urwid
ui = urwid.curses_display.Screen()
def run():
cols, rows = ui.get_cols_rows()
txt = urwid.Text("Hello World", align="center")
fill = urwid.Filler( txt )
canvas = fill.render( (cols, rows) )
ui.draw_screen( (cols, rows), canvas )
while not ui.get_input():
pass
ui.run_wrapper( run )
- get_cols_rows
is used to get the dimensions from the terminal and store them as "cols"
and "rows".
- A Text widget is created containing
the string "Hello World". It is set to display with "center" alignment.
Text widgets are a kind of FlowWidget.
Flow widgets can fill one or more rows, depending on their content and
the number of columns available. Text widgets use more than one row when
they contain newline characters or when the text must be split across rows.
- A Filler widget is created to
wrap the text widget. Filler widgets are a kind of
BoxWidget. Box widgets have a fixed
number of columns and rows displayed. This widget will pad the "Hello World"
text widget until it fills the required number of rows.
- A canvas is created by calling the
render function on the topmost
widget. The filler render function will call the render function
of the "Hello World" text widget and combine its canvas with
padding rows to fill the terminal window.
Flow widgets and box widgets are not interchangeable. The first parameter
of the render function of a box widget is a two-element tuple (columns,
rows) and the first parameter of the render function of a flow widget is
a one-element tuple (columns, ).
This difference makes sure that when the wrong type of widget is used,
such as a box widget inside a filler widget, a ValueError exception will
be thrown.
This program displays the string "Hello World" in the center of the screen.
It uses different attributes for the text, the space on either side
of the text and the space above and below the text. It waits for
a keypress before exiting.
import urwid.curses_display
import urwid
ui = urwid.curses_display.Screen()
ui.register_palette( [
('banner', 'black', 'light gray', ('standout', 'underline')),
('streak', 'black', 'dark red', 'standout'),
('bg', 'black', 'dark blue'),
] )
def run():
cols, rows = ui.get_cols_rows()
txt = urwid.Text(('banner', " Hello World "), align="center")
wrap1 = urwid.AttrWrap( txt, 'streak' )
fill = urwid.Filler( wrap1 )
wrap2 = urwid.AttrWrap( fill, 'bg' )
canvas = wrap2.render( (cols, rows) )
ui.draw_screen( (cols, rows), canvas )
while not ui.get_input():
pass
ui.run_wrapper( run )
- After creating the
curses_display.Screen object
and before calling run_wrapper,
register_palette is called
to set up some attributes:
- "banner" is black text on a light gray background, or reversed attributes
and underlined in monochrome mode
- "streak" is black text on a dark red background, or reversed attributes
in monochrome mode
- "bg" is black text on a dark blue background, or normal in
monochrome mode
- A Text widget is created containing
the string " Hello World " with attribute "banner". The attributes of text
in a Text widget is set by using a (attribute, text) tuple instead of a
simple text string.
- An AttrWrap widget is created to
wrap the text widget with attribute "streak". AttrWrap widgets will set
the attribute of everything that they wrap that does not already have an
attribute set. In this case the text has an attribute, so only the areas
around the text used for alignment will be have the new attribute.
- A Filler widget is created to
wrap the AttrWrap widget and fill the rows above and below it.
- A second AttrWrap widget is created to
wrap the filler widget with attribute "bg".
- A canvas is created by calling the
render function on the topmost
widget.
AttrWrap widgets will behave like flow widgets or box widgets depending on
how they are called. The filler widget treats the first AttrWrap widget as
a flow widget when calling its render function, so the AttrWrap widget calls
the text widget's render function the same way. The second AttrWrap is
used as the topmost widget and treated as a box widget, so it calls the
filler render function in the same way.
This program displays the string "Hello World" in the center of the screen.
It uses different attributes for the text, the space on either side
of the text and the space above and below the text. When the window is
resized it will repaint the screen, and it will exit when Q is pressed.
import urwid.curses_display
import urwid
ui = urwid.curses_display.Screen()
ui.register_palette( [
('banner', 'black', 'light gray', ('standout', 'underline')),
('streak', 'black', 'dark red', 'standout'),
('bg', 'black', 'dark blue'),
] )
def run():
cols, rows = ui.get_cols_rows()
txt = urwid.Text(('banner', " Hello World "), align="center")
wrap1 = urwid.AttrWrap( txt, 'streak' )
fill = urwid.Filler( wrap1 )
wrap2 = urwid.AttrWrap( fill, 'bg' )
while True:
canvas = wrap2.render( (cols, rows) )
ui.draw_screen( (cols, rows), canvas )
keys = ui.get_input()
if "q" in keys or "Q" in keys:
break
if "window resize" in keys:
cols, rows = ui.get_cols_rows()
ui.run_wrapper( run )
The get_input function will
return "window resize" among keys pressed when the window is resized. It
is a good idea to check for uppercase and lowercase letters on input
to avoid confusing users.
2. Conversation Example
This program asks for your name then responds "Nice to meet you, (your name)."
import urwid.curses_display
import urwid
ui = urwid.curses_display.Screen()
def run():
cols, rows = ui.get_cols_rows()
ask = urwid.Edit("What is your name?\n")
fill = urwid.Filler( ask )
reply = None
while True:
canvas = fill.render( (cols, rows), focus=True )
ui.draw_screen( (cols, rows), canvas )
keys = ui.get_input()
for k in keys:
if k == "window resize":
cols, rows = ui.get_cols_rows()
continue
if reply is not None:
return
if k == "enter":
reply = urwid.Text( "Nice to meet you,\n"+
ask.edit_text+"." )
fill.body = reply
if fill.selectable():
fill.keypress( (cols, rows), k )
ui.run_wrapper( run )
- An Edit widget is created with the
caption "What is your name?". A newline at the end of the caption makes
the user input start on the next row.
- A Filler widget is created to wrap
the edit widget. Its render
function is called to create the canvas. The render function is called with
the optional parameter "focus" set to True. This parameter allows the
wrapped Edit widget to render its cursor.
- Keys are processed one at a time. Most keys are sent to the Filler widget's
keypress function which will
call the Edit widget's keypress
function to handle the key.
- Once the ENTER key is pressed the wrapped object in the Filler widget
is changed to a reply text.
- Any keypress then causes the program to exit.
The Edit widget has many capabilities. It lets you make corrections and move
the cursor around with the HOME, END and arrow keys. It is based on the Text
widget so it supports the same wrapping and alignment modes.
What is your name?
Arthur, King of the
Britons
What is your name?
Arthur, King of the
Britons
This program asks for your name and responds "Nice to meet you, (your name)"
while you type your name. F8 exits.
import urwid.curses_display
import urwid
class Conversation(object):
def __init__(self):
self.items = urwid.SimpleListWalker(
[self.new_question()])
self.listbox = urwid.ListBox(self.items)
instruct = urwid.Text("Press F8 to exit.")
header = urwid.AttrWrap( instruct, 'header' )
self.top = urwid.Frame(self.listbox, header)
def main(self):
self.ui = urwid.curses_display.Screen()
self.ui.register_palette([
('header', 'black', 'dark cyan', 'standout'),
('I say', 'default', 'default', 'bold'),
])
self.ui.run_wrapper( self.run )
def run(self):
size = self.ui.get_cols_rows()
while True:
self.draw_screen( size )
keys = self.ui.get_input()
if "f8" in keys:
break
for k in keys:
if k == "window resize":
size = self.ui.get_cols_rows()
continue
self.top.keypress( size, k )
if keys:
name = self.items[0].edit_text
self.items[1:2] = [self.new_answer(name)]
def draw_screen(self, size):
canvas = self.top.render( size, focus=True )
self.ui.draw_screen( size, canvas )
def new_question(self):
return urwid.Edit(('I say',"What is your name?\n"))
def new_answer(self, name):
return urwid.Text(('I say',"Nice to meet you, "+name+"\n"))
Conversation().main()
- In the __init__ function a list called self.items is created. It
contains an Edit widget with the caption "What is your name?".
- A ListBox widget called
self.listbox is created that is passed the self.items list.
This ListBox widget will display and scroll through the widgets in that list.
ListBox widgets default to using the first item in the list as the focus.
- A Frame widget called self.top
is created that contains self.listbox and some header text. Frame widgets
wrap around a box widget and may have header and footer flow widgets.
The header and footer are always displayed. The contained box widget uses the
remaining space in between.
- When a key is pressed the reply text is inserted or updated in
self.items. This updated text will be displayed by self.listbox.
When changing the contents of ListBox widgets remember to use in-place
editing operations on the list, eg. "list = list + [something]" will not work,
use "list += [something]" instead. The former code will create a new list
but the ListBox will still be displaying the old list.
Press F8 to exit.
What is your name?
Press F8 to exit.
What is your name?
Tim t
Nice to meet you, Tim
t
Press F8 to exit.
What is your name?
Tim the Ench
Nice to meet you, Tim
the Ench
Press F8 to exit.
What is your name?
Tim the Enchanter
Nice to meet you, Tim
the Enchanter
This program asks for your name and responds "Nice to meet you, (your name)."
It then asks again, and again. Old values may be changed and the responses
will be updated when you press ENTER. F8 exits.
Update the previous program with this code:
def run(self):
size = self.ui.get_cols_rows()
while True:
self.draw_screen( size )
keys = self.ui.get_input()
if "f8" in keys:
break
for k in keys:
if k == "window resize":
size = self.ui.get_cols_rows()
continue
self.keypress( size, k )
def keypress(self, size, k):
if k == "enter":
widget, pos = self.listbox.get_focus()
if not hasattr(widget,'get_edit_text'):
return
answer = self.new_answer( widget.get_edit_text() )
if pos == len(self.items)-1:
self.items.append( answer )
self.items.append( self.new_question() )
else:
self.items[pos+1:pos+2] = [answer]
self.listbox.set_focus( pos+2, coming_from='above' )
widget, pos = self.listbox.get_focus()
widget.set_edit_pos(0)
else:
self.top.keypress( size, k )
- In this version only the ENTER key receives special attention. When the
user presses ENTER:
- The widget in focus and its current position is retrieved by calling the
get_focus function.
- If the widget in focus does not have an edit_text attribute, then it
is not one of the Edit widgets we are interested in.
One of the Text widgets might receive focus
if it covers the entire visible area of the ListBox widget and there is
no Edit widget to take focus. While this is unlikely, it should be handled
or the program will fail when trying to call
get_edit_text.
- If the current position is at the end of the list, a response is
appended followed by a new question. If the current position is not at the
end then a previous response is replaced with an updated one.
- The focus is moved down two positions to the next question by calling
set_focus.
- Finally, the cursor position within the new focus widget is moved to
the far left by calling
set_edit_pos.
- All other keys are passed to the top widget to handle. The ListBox widget
does most of the hard work:
- UP and DOWN will change the focus and/or scroll the widgets in the list
box.
- PAGE UP and PAGE DOWN will try to move the focus one screen up or down.
- The cursor's column is maintained as best as possible when moving
from one Edit widget to another.
Press F8 to exit.
What is your name?
Abe
Nice to meet you, Abe
What is your name?
Bob
Press F8 to exit.
Nice to meet you, Abe
What is your name?
Bob
Nice to meet you, Bob
What is your name?
Carl
Nice to meet you, Carl
What is your name?
Press F8 to exit.
Nice to meet you, Bob
What is your name?
Carl
Nice to meet you, Carl
What is your name?
Dave
Nice to meet you, Dave
What is your name?
3. Zen of ListBox
The
ListBox
is a box widget that contains flow widgets. Its contents
are displayed stacked vertically, and the ListBox allows the user to scroll
through its content. One of the flow widgets displayed
in the ListBox is the focus widget. The ListBox passes key presses to the
focus widget to allow the user to interact with it. If the
focus widget does not handle a keypress then the ListBox may handle the
keypress by scrolling and/or selecting another widget to become the focus
widget.
The ListBox tries to do the most sensible thing when scrolling and
changing focus. When the widgets displayed are all Text widgets or
other unselectable widgets then the ListBox will behave like a web browser
does when the user presses UP, DOWN, PAGE UP and PAGE DOWN: new text is
immediately scrolled in from the top or bottom. The ListBox chooses one of the
visible widgets as its focus widget when scrolling. When scrolling up the
ListBox chooses the topmost widget as the focus, and when scrolling down
the ListBox chooses the bottommost widget as the focus.
When all the widgets displayed are not selectable the user would typically
have no way to tell which widget is in focus, but if we wrap the widgets with
AttrWrap we can see what is happening while the focus changes:
CONTENT = [ urwid.AttrWrap( w, None, 'reveal focus' ) for w in [
urwid.Text("This is a text string that is fairly long"),
urwid.Divider("-"),
urwid.Text("Short one"),
urwid.Text("Another"),
urwid.Divider("-"),
urwid.Text("What could be after this?"),
urwid.Text("The end."),
] ]
Pressed:
This is a text
string that is
fairly long
---------------
Short one
Another
Pressed: down
string that is
fairly long
---------------
Short one
Another
---------------
Pressed: down
fairly long
---------------
Short one
Another
---------------
What could be
Pressed: down
---------------
Short one
Another
---------------
What could be
after this?
Pressed: up
fairly long
---------------
Short one
Another
---------------
What could be
Pressed: up
string that is
fairly long
---------------
Short one
Another
---------------
The ListBox remembers the location of the widget in focus as either an
"offset" or an "inset". An offset is the number of rows between the top
of the ListBox and the beginning of the focus widget. An offset of zero
corresponds to a widget with its top aligned with the top of the ListBox.
An inset is the fraction of rows of the focus widget
that are "above" the top of the ListBox and not visible.
The ListBox uses this method of remembering the focus widget location
so that when the ListBox is resized the text displayed will stay
roughly aligned with the top of the ListBox.
Pressed:
string that is
fairly long
--------------------
Short one
Another
--------------------
What could be after
this?
Pressed:
This is a text string
that is fairly long
-------------------------
Short one
Another
-------------------------
Pressed:
This is a
text string
that is
fairly long
-----------
Short one
Another
-----------
What could
be after
this?
The end.
When there are selectable widgets in the ListBox the focus will move
between the selectable widgets, skipping the unselectable widgets.
The ListBox will try to scroll all the rows of a selectable widget into
view so that the user can see the new focus widget in its entirety.
This behavior can be used to bring more than a single widget into view
by using composite widgets to combine a selectable widget with other
widgets that should be displayed at the same time.
While the ListBox stores the location of its focus widget, it
does not directly store the actual focus widget or other contents of the
ListBox. The storage of a ListBox's content is delegated to a "List Walker"
object. If a list of widgets is passed to the ListBox constructor then it
creates a
SimpleListWalker
object to manage the list.
When the ListBox is
rendering a canvas or
handling input it will:
- Call the
get_focus
method of its list walker object.
This method will return the focus widget and a position object.
- Optionally call the
get_prev
method of its List Walker object
one or more times, initially passing
the focus position and then passing the new position returned on each
successive call. This method will return the widget and position object
"above" the position passed.
- Optionally call the
get_next
method of its List Walker object
one or more times, similarly, to collect widgets and position objects
"below" the focus position.
- Optionally call the
set_focus
method passing one of the position
objects returned in the previous steps.
This is the only way the ListBox accesses its contents, and it will not
store copies of any of the widgets or position objects beyond the current
rendering or input handling operation.
The SimpleListWalker stores a list of widgets, and uses integer indexes into
this list as its position objects. It stores the focus
position as an integer, so if you insert a widget into the list above the
focus position then you need to remember to increment the focus position in
the SimpleListWalker object or the contents of the ListBox will shift.
A custom List Walker object may be passed to the ListBox constructor instead
of a plain list of widgets. List Walker objects must implement the
List Walker interface.
The
fib.py
example program demonstrates a custom list walker that doesn't
store any widgets. It uses a tuple of two successive Fibonacci numbers
as its position objects and it generates Text widgets to display the numbers
on the fly.
The result is a ListBox that can scroll through an unending list of widgets.
The
edit.py
example program demonstrates a custom list walker that
loads lines from a text file only as the user scrolls them into view.
This allows even huge files to be opened almost instantly.
The
browse.py
example program demonstrates a custom list walker that
uses a tuple of strings as position objects, one for the parent directory
and one for the file selected. The widgets are cached in a separate class
that is accessed using a dictionary indexed by parent directory names.
This allows the directories to be read only as required. The custom list
walker also allows directories to be hidden from view when they are
"collapsed".
The easiest way to change the current ListBox focus is to call the
set_focus method.
This method doesn't require that you know the ListBox's
current dimensions (maxcol, maxrow). It will wait until the next call to
either keypress or render to complete setting the offset and inset values
using the dimensions passed to that method.
The position object passed to set_focus must be compatible with the List
Walker object that the ListBox is using. For SimpleListWalker the position
is the integer index of the widget within the list.
The coming_from parameter should be set if you know that the old position
is "above" or "below" the previous position. When the ListBox completes
setting the offset and inset values it tries to find the old widget among
the visible widgets. If the old widget is still visible, if will try to
avoid causing the ListBox contents to scroll up or down from its previous
position. If the widget is not visible, then the ListBox will:
- Display the new focus at the bottom of the ListBox if coming_from is
"above".
- Display the new focus at the top of the ListBox if coming_from is "below".
- Display the new focus in the middle of the ListBox if coming_from is None.
If you know exactly where you want to display the new focus widget within
the ListBox you may call
set_focus_valign.
This method lets you specify the
"top", "bottom", "middle", a relative position or the exact number of rows
from the top or bottom of the ListBox.
4. Combining Widgets
Pile
widgets are used to combine multiple widgets by stacking them
vertically. A Pile can manage selectable widgets by keeping track of which
widget is in focus and it can handle moving the focus between widgets when
the user presses the UP and DOWN keys. A Pile will also work well when used
within a ListBox.
A Pile is selectable only if its focus widget is selectable. If you create
a Pile containing one Text widget and one Edit widget the Pile will
choose the Edit widget as its default focus widget.
To change the pile's focus widget you can call
set_focus.
Columns
widgets may be used to arrange either flow widgets or box widgets
horizontally into columns. Columns widgets will manage selectable widgets
by keeping track of which column is in focus and it can handle moving the
focus between columns when the user presses the LEFT and RIGHT keys.
Columns widgets also work well when used within a ListBox.
Columns widgets are selectable only if the column in focus is selectable.
If a focus column is not specified the first selectable widget will be
chosen as the focus column. The
set_focus
method may be used to select the focus column.
The
GridFlow
widget is a flow widget designed for use with
Button,
CheckBox and
RadioButton widgets.
It renders all the widgets it contains the same width and it arranges them
from left to right and top to bottom.
The GridFlow widget uses Pile, Columns, Padding and Divider widgets to build
a display widget that will handle the keyboard input and rendering. When the
GridFlow widget is resized it regenerates the display widget to accommodate
the new space.
The Overlay widget is a box widget that
contains two other box widgets. The bottom widget is rendered the full size
of the Overlay widget and the top widget is placed on top, obscuring an area
of the bottom widget. This widget can be used to create effects such as
overlapping "windows" or pop-up menus.
The Overlay widget always treats the top widget as the one in focus. All
keyboard input will be passed to the top widget.
If you want to use a flow
flow widget for the top widget, first wrap the flow widget with a
Filler widget.
5. Creating Custom Widgets
The easiest way to create a custom widget is to modify an existing widget.
This can be done by either subclassing the original widget or by wrapping it.
Subclassing is appropriate when you need to interact at a very low level
with the original widget, such as if you are creating a custom edit widget
with different behavior than the usual Edit widgets. If you are creating
a custom widget that doesn't need tight coupling with the original widget,
such as a widget that displays customer address information, then wrapping
is more appropriate.
The WidgetWrap class simplifies
wrapping existing widgets. You can create a custom widget simply by
creating a subclass of WidgetWrap and passing a widget into WidgetWrap's
constructor.
This is an example of a custom widget that uses WidgetWrap:
class QuestionnaireItem( urwid.WidgetWrap ):
def __init__(self):
self.options = []
unsure = urwid.RadioButton( self.options, "Unsure" )
yes = urwid.RadioButton( self.options, "Yes" )
no = urwid.RadioButton( self.options, "No" )
display_widget = urwid.GridFlow( [unsure, yes, no],
15, 3, 1, 'left' )
urwid.WidgetWrap.__init__(self, display_widget)
def get_state(self):
for o in self.options:
if o.get_state() is True:
return o.get_label()
The above code creates a group of RadioButtons and provides a method to
query the state of the buttons.
Wrapped widgets may also override the standard widget methods. These methods
are described in following sections.
Any object that follows the
Widget interface definition
may be used as a widget. Box widgets must implement
selectable
and
render
methods, and flow widgets must implement selectable, render and
rows
methods.
class Pudding( urwid.FlowWidget ):
def selectable( self ):
return False
def rows( self, (maxcol,), focus=False ):
return 1
def render( self, (maxcol,), focus=False ):
num_pudding = maxcol / len("Pudding")
return urwid.TextCanvas(["Pudding"*num_pudding])
class BoxPudding( urwid.BoxWidget ):
def selectable( self ):
return False
def render( self, (maxcol, maxrow), focus=False ):
num_pudding = maxcol / len("Pudding")
return urwid.TextCanvas(
["Pudding"*num_pudding] * maxrow)
The above code implements two widget classes. Pudding is a flow widget and
BoxPudding is a box widget. Pudding will render as much "Pudding" as will
fit in a single row, and BoxPudding will render as much "Pudding" as will
fit into the entire area given.
It is not strictly necessary to inherit from
BoxWidget or
FlowWidget, but doing so does add
some documentation to your code.
Note that the rows and render methods' focus parameter must have a default
value of False. Also note that for flow widgets the number of rows returned
by the rows method must match the number of rows rendered by the render
method.
In most cases it is easier to let other widgets handle the rendering and
row calculations for you:
class NewPudding( urwid.FlowWidget ):
def selectable( self ):
return False
def rows( self, (maxcol,), focus=False ):
w = self.display_widget( (maxcol,), focus )
return w.rows( (maxcol,), focus )
def render( self, (maxcol,), focus=False ):
w = self.display_widget( (maxcol,), focus )
return w.render( (maxcol,), focus )
def display_widget( self, (maxcol,), focus ):
num_pudding = maxcol / len("Pudding")
return urwid.Text( "Pudding"*num_pudding )
The NewPudding class behaves the same way as the Pudding class above, but in
NewPudding you can change the way the widget appears by modifying only the
display_widget method, whereas in the Pudding class you may have to modify both
the render and rows methods.
To improve the efficiency of your Urwid application you should be careful
of how long your rows methods take to execute. The rows methods may be called
many times as part of input handling and rendering operations. If you are
using a display widget that is time consuming to create you should consider
caching it to reduce its impact on performance.
It is possible to create a widget that will behave as either a flow widget
or box widget depending on what is required:
class MultiPudding( urwid.Widget ):
def selectable( self ):
return False
def rows( self, (maxcol,), focus=False ):
return 1
def render( self, size, focus=False ):
if len(size) == 1:
(maxcol,) = size
maxrow = 1
else:
(maxcol, maxrow) = size
num_pudding = maxcol / len("Pudding")
return urwid.TextCanvas(
["Pudding"*num_pudding] * maxrow )
MultiPudding will work in place of either Pudding or BoxPudding above. The
number of elements in the size tuple determines whether the containing widget
is expecting a flow widget or a box widget.
Selectable widgets such as Edit and Button widgets allow the user to
interact with the application. A widget is selectable if its selectable
method returns True. Selectable widgets must implement the
keypress
method to handle keyboard input.
class SelectablePudding( urwid.FlowWidget ):
def __init__( self ):
self.pudding = "pudding"
def selectable( self ):
return True
def rows( self, (maxcol,), focus=False ):
return 1
def render( self, (maxcol,), focus=False ):
num_pudding = maxcol / len(self.pudding)
pudding = self.pudding
if focus:
pudding = pudding.upper()
return urwid.TextCanvas( [pudding*num_pudding] )
def keypress( self, (maxcol,), key ):
if len(key)>1:
return key
if key.lower() in self.pudding:
# remove letter from pudding
n = self.pudding.index(key.lower())
self.pudding = self.pudding[:n]+self.pudding[n+1:]
if not self.pudding:
self.pudding = "pudding"
else:
return key
The SelectablePudding widget will display its contents in uppercase when it
is in focus, and it allows the user to "eat" the pudding by pressing each of
the letters P, U, D, D, I, N and G on the keyboard. When the user has "eaten"
all the pudding the widget will reset to its initial state.
Note that keys that are unhandled in the keypress method are returned so that
another widget may be able to handle them. This is a good convention to follow
unless you have a very good reason not to. In this case the UP and DOWN keys
are returned so that if this widget is in a ListBox the ListBox will behave as
the user expects and change the focus or scroll the ListBox.
Widgets that display the cursor must implement the
get_cursor_coords
method. Similar to the rows method for flow widgets, this method lets other
widgets make layout decisions without rendering the entire widget. The
ListBox widget in particular uses get_cursor_coords to make sure that the
cursor is visible within its focus widget.
class CursorPudding( urwid.FlowWidget ):
def __init__( self ):
self.cursor_col = 0
def selectable( self ):
return True
def rows( self, (maxcol,), focus=False ):
return 1
def render( self, (maxcol,), focus=False ):
num_pudding = maxcol / len("Pudding")
cursor = None
if focus:
cursor = self.get_cursor_coords((maxcol,))
return urwid.TextCanvas(
["Pudding"*num_pudding], [], cursor )
def get_cursor_coords( self, (maxcol,) ):
col = min(self.cursor_col, maxcol-1)
return col, 0
def keypress( self, (maxcol,), key ):
if key == 'left':
col = self.cursor_col -1
elif key == 'right':
col = self.cursor_col +1
else:
return key
self.cursor_x = max(0, min( maxcol-1, col ))
CursorPudding will let the user move the cursor through the widget by
pressing LEFT and RIGHT. The cursor must only be added to the canvas when
the widget is in focus. The get_cursor_coords method must always return
the same cursor coordinates that render does.
A widget displaying a cursor may choose to implement
get_pref_col.
This method returns the preferred column for the cursor, and is called when
the focus is moving up or down off this widget.
Another optional method is
move_cursor_to_coords.
This method allows other widgets to try to position the cursor within this
widget. The ListBox widget uses move_cursor_to_coords when changing focus and
when the user pressed PAGE UP or PAGE DOWN. This method must return True on
success and False on failure. If the cursor may be placed at any position
within the row specified (not only at the exact column specified) then this
method must move the cursor to that position and return True.
def get_pref_col( self, (maxcol,) ):
return self.cursor_x
def move_cursor_to_coords( self, (maxcol,), col, row ):
assert row == 0
self.cursor_x = col
return True