Repository: ManimCommunity/manim
File: manim/mobject/number_line.py (Python)

Code before:
    def get_tick(self, x, size=None):
        if size is None:
            size = self.tick_size
        result = Line(size * DOWN, size * UP)
        result.rotate(self.get_angle())
        result.move_to(self.number_to_point(x))
        result.match_style(self)
        return result

    def get_tick_marks(self):
        return VGroup(self.ticks)

    def get_tick_range(self):
        if self.include_tip:
            x_max = self.x_max
        else:
            x_max = self.x_max + 1e-6
        return np.arange(self.x_min, x_max, self.x_step)

    def number_to_point(self, number):
        alpha = float(number - self.x_min) / (self.x_max - self.x_min)
        return interpolate(self.get_start(), self.get_end(), alpha)

    def point_to_number(self, point):
        start, end = self.get_start_and_end()
        unit_vect = normalize(end - start)
        proportion = fdiv(
            np.dot(point - start, unit_vect),
            np.dot(end - start, unit_vect),
        )
        return interpolate(self.x_min, self.x_max, proportion)

    def n2p(self, number):
        """Abbreviation for number_to_point"""
        return self.number_to_point(number)

    def p2n(self, point):
        """Abbreviation for point_to_number"""
        return self.point_to_number(point)

    def get_unit_size(self):
        return self.get_length() / (self.x_max - self.x_min)

    def get_unit_vector(self):
        return super().get_unit_vector() * self.unit_size

    def get_number_mobject(self, x, direction=None, buff=None, **number_config):
        number_config = merge_dicts_recursively(
            self.decimal_number_config, number_config
        )
        if direction is None:

Review comment (suggestion):
Currently, the first ticks are not added since `np.arange` does include the max_value. This causes the default axes to look like this:
![image](https://user-images.githubusercontent.com/70682032/120594610-33f24100-c40f-11eb-9185-81bd447719f6.png)

Following the code from `include_tip` fixes this issue.
```suggestion
        x_min_segment = np.arange(start_point, np.abs(self.x_min) + 1e-6, self.x_step) * -1
```

Code after:
        self.ticks = ticks

    def get_tick(self, x, size=None):
        if size is None:
            size = self.tick_size
        result = Line(size * DOWN, size * UP)
        result.rotate(self.get_angle())
        result.move_to(self.number_to_point(x))
        result.match_style(self)
        return result

    def get_tick_marks(self):
        return VGroup(self.ticks)

    def get_tick_range(self):
        if self.include_tip:
            x_max = self.x_max
        else:
            x_max = self.x_max + 1e-6

        # Handle cases where min and max are both positive or both negative
        if self.x_min < x_max < 0 or self.x_max > self.x_min > 0:
            return np.arange(self.x_min, x_max, self.x_step)

        start_point = 0
        if self.exclude_origin_tick:
            start_point += self.x_step

        x_min_segment = (
            np.arange(start_point, np.abs(self.x_min) + 1e-6, self.x_step) * -1
        )
        x_max_segment = np.arange(start_point, x_max, self.x_step)

        return np.unique(np.concatenate((x_min_segment, x_max_segment)))

    def number_to_point(self, number):
        alpha = float(number - self.x_min) / (self.x_max - self.x_min)
        return interpolate(self.get_start(), self.get_end(), alpha)

    def point_to_number(self, point):
        start, end = self.get_start_and_end()
        unit_vect = normalize(end - start)
        proportion = fdiv(
            np.dot(point - start, unit_vect),
            np.dot(end - start, unit_vect),
        )
        return interpolate(self.x_min, self.x_max, proportion)

    def n2p(self, number):
        """Abbreviation for number_to_point"""
        return self.number_to_point(number)