What Is the Purpose of a Backslash at the End of a Line

What is the purpose of a backslash at the end of a line?

Yep, it's exactly the same and this is the point of the backslash — it escapes the newline, allowing this long line to be split in two. An alternative is to use parentheses:

from sqlalchemy.ext.declarative import (declarative_base,
      AbstractConcreteBase)

While this is a syntax error:

from sqlalchemy.ext.declarative import declarative_base,
      AbstractConcreteBase

what does backslash means at the end of line

In the context of line-oriented text, especially source code for some programming languages, it is often used at the end of a line to indicate that the trailing newline character should be ignored, so that the following line is treated as if it were part of the current line. In this context it may be called a "continuation". The GNU make manual says, "We split each long line into two lines using backslash-newline; this is like using one long line, but is easier to read."

Backslash in c source file

It's a line-continuation escape. It means the compiler will consider the next line as a part of the current line.

It makes the code you show in practice being

frame_rate = (float)
                ( ( ( frames * media_timescale) + ( media_duration >> 1 ) ) /
                 media_duration);

There's no real need for it in this case though, except as maybe some style-guide followed by the author had it as a requirement.

Line continuation is needed to define "multi-line" macros, and are also often used for long strings. But besides those places, it serves no real purpose.

Why do multi-line macros have backslashes at the end of each line?

It's a line continuation character.

There should be nothing else after it (aside from an end of line character), including white space.

It's particularly useful for macros as it adds clarity.

(Very, very occasionally - especially in old code - you'll see the trigraph sequence ??/ in place of \. These days though it's more of an interviewers' trick question.)

What does back slash following an equation mark in function argument do in Python

Simple answer is, you don't need the \ at all (in this case**). In python, \ is a line continuation character. All it does is make the line and the following line behave as if it were all on one line. It is only in the code for readability, and it won't cause any problems if you take it out.

**The backslash is not required here because it is a variable initialization. If you were using the backslash for something else such as continuing a string on another line, removing it will raise exceptions.

meaning of back slash at the end of the every line in .js file for html tags

The code represents a JavaScript string object containing raw HTML. The \ character allows newlines to be inserted in the string without the need of manual concatenation.

In C, is the backslash character (\) required when one needs to split arguments of functions or logical conditions into multiple lines?

The slashes are optional except for defining multi line macros as Gerhardh mentioned.

#include <stdio.h>

//valid macro
#define BAR(x, y, z) printf("%d %c %f\n", \
                            x, \
                            y, \
                            z);

//invalid macro, this won't compile if uncommented
/*
#define BAR(x, y, z) printf("%d %c %f\n",
x,
    y,
    z);
*/

void foo(int x, char y, float z) {
    printf("%d %c %f\n", x, y, z);
}

int main() {
    //valid
    foo(5, \
        'c', \
        0.0f);

    //also valid
    foo(5,
        'c',
        0.0f);

    //even use of the macro without slashes is valid
    BAR(5,
        'c',
        0.0f);

    return 0;
}

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