| << Chapter < Page | Chapter >> Page > |
This is the key that causes the cursor to go down to the next line and return to the left side of the editing window.
For example, when creating the text shown in Figure 1 using a text editor on my Windows computer, I pressed the Enter key immediately following the -->for each line. This produced a newline in each case.
| Figure 1 . Two physical lines. |
|---|
I will end the line here -->and end the next line here --> |
A logical line may be the same as a physical line , or line joining rules (described later) can be used to construct a logical line from two or more physical lines.
A statement cannot cross logical line boundaries except where the syntax allows for the newline character, such as in compound statements . I will show you an example of a compound statement later in this module.
We learned about comments in an earlier module. To summarize, a comment starts with a hash character (#) that is not part of a string literal (we also learned about string literals in an earlier module) . The comment ends at the end of the physical line.
You can join two or more physical lines to produce a logical line , using the backslash character as shown in Listing 1 .
| Listing 1 . Explicit line joining. |
|---|
a = 3
b = 4# construct c=a+b
c \= \
a \+ \
bprint(c)
# the output is 7 |
When a physical line ends in a backslash that is not part of a string literal or comment, that line is joined with the following physical line forming a single logical line .
The backslash and the following end-of-line character(s) are ignored by the interpreter and do not become part of the logical line.
In Listing 1 , the expression c=a+b is created by joining five consecutive physical lines to create one logical line .
Obviously, this is not how you would want to write a long script, but it is not unusual to break long expressions into two or more physical lines to makethem fit onto a prescribed page width.
You must make certain that no space characters follow the backslash.
You may not place a comment following the backslash, and a backslash does not continue a comment.
A backslash is illegal elsewhere on a line except inside a string literal.
Expressions in parentheses, square brackets, or curly brackets can be split over more than one physical line without using backslashes as shown in Listing 2 .
| Listing 2 . Implicit line joining. |
|---|
a = 3
b = 4c = (a # continue on next line
+ b)print(c)
# the output is 7 |
You can also place a comment on a line that is being continued implicitly as shown in the third line of Listing 2 .
Also, you can indent the continuation line however you want. This is very useful for making the code more readable.
Lines containing only spaces, tabs, form feeds, and comments are ignored in scripts, but the behavior may be different in interactive mode, depending on theimplementation.
An example of some spaces and blank lines is shown in Listing 3 .
Notification Switch
Would you like to follow the 'Itse 1359 introduction to scripting languages: python' conversation and receive update notifications?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|