How to Format Text in Python

Aspose.Slides FOSS for Python provides fine-grained text formatting through the PortionFormat class. A Portion is the smallest independent unit of text; it maps to a single formatting run within a paragraph. This guide shows how to apply bold, italic, font size, and color formatting to text in a presentation.

Step-by-Step Guide

Step 1: Install the Package

pip install aspose-slides-foss

Step 2: Add a Shape with a Text Frame

Before formatting text, a shape must contain a TextFrame. Use shape.add_text_frame() to create one.

import aspose.slides_foss as slides
from aspose.slides_foss import ShapeType
from aspose.slides_foss.export import SaveFormat

with slides.Presentation() as prs:
    slide = prs.slides[0]
    shape = slide.shapes.add_auto_shape(ShapeType.RECTANGLE, 50, 50, 500, 150)
    tf = shape.add_text_frame("Default text: will be formatted")
    prs.save("output.pptx", SaveFormat.PPTX)

Step 3: Access the TextFrame

shape.add_text_frame() returns the TextFrame object. You can also retrieve it later via shape.text_frame.

tf = shape.text_frame          # if the frame already exists
tf = shape.add_text_frame("") # creates a new frame

A TextFrame contains a list of Paragraph objects (tf.paragraphs). Each Paragraph contains Portion objects (paragraph.portions).

Step 4: Apply Bold and Italic Formatting

Use portion_format.font_bold and portion_format.font_italic. These properties accept NullableBool.TRUE, NullableBool.FALSE, or NullableBool.NOT_DEFINED (inherit from master).

import aspose.slides_foss as slides
from aspose.slides_foss import ShapeType, NullableBool
from aspose.slides_foss.export import SaveFormat

with slides.Presentation() as prs:
    slide = prs.slides[0]
    shape = slide.shapes.add_auto_shape(ShapeType.RECTANGLE, 50, 50, 500, 150)
    tf = shape.add_text_frame("Bold and italic text")

    fmt = tf.paragraphs[0].portions[0].portion_format
    fmt.font_bold = NullableBool.TRUE
    fmt.font_italic = NullableBool.TRUE

    prs.save("bold-italic.pptx", SaveFormat.PPTX)

Step 5: Set Font Size and Color

Set portion_format.font_height for size (in points) and use fill_format for color.

import aspose.slides_foss as slides
from aspose.slides_foss import ShapeType, NullableBool, FillType
from aspose.slides_foss.drawing import Color
from aspose.slides_foss.export import SaveFormat

with slides.Presentation() as prs:
    slide = prs.slides[0]
    shape = slide.shapes.add_auto_shape(ShapeType.RECTANGLE, 50, 50, 500, 150)
    tf = shape.add_text_frame("Large corporate-blue heading")

    fmt = tf.paragraphs[0].portions[0].portion_format
    fmt.font_height = 32                          # 32pt font
    fmt.font_bold = NullableBool.TRUE
    fmt.fill_format.fill_type = FillType.SOLID
    fmt.fill_format.solid_fill_color.color = Color.from_argb(255, 0, 70, 127)

    prs.save("colored-text.pptx", SaveFormat.PPTX)

Color.from_argb(alpha, red, green, blue) accepts values 0–255 for each channel.

Step 6: Multiple Portions in One Paragraph

A single paragraph can contain multiple portions with different formatting. Add a new Portion to a paragraph’s portions collection:

import aspose.slides_foss as slides
from aspose.slides_foss import ShapeType, NullableBool, FillType
from aspose.slides_foss.drawing import Color
from aspose.slides_foss.export import SaveFormat

with slides.Presentation() as prs:
    slide = prs.slides[0]
    shape = slide.shapes.add_auto_shape(ShapeType.RECTANGLE, 50, 50, 600, 100)
    tf = shape.add_text_frame("")  # start with empty frame

    paragraph = tf.paragraphs[0]

    # First portion: normal text
    portion1 = paragraph.portions[0]
    portion1.text = "Normal text followed by "
    portion1.portion_format.font_height = 20

    # Second portion: bold red text
    portion2 = slides.Portion()
    portion2.text = "bold red text"
    portion2.portion_format.font_height = 20
    portion2.portion_format.font_bold = NullableBool.TRUE
    portion2.portion_format.fill_format.fill_type = FillType.SOLID
    portion2.portion_format.fill_format.solid_fill_color.color = Color.from_argb(255, 200, 0, 0)
    paragraph.portions.add(portion2)

    prs.save("mixed-format.pptx", SaveFormat.PPTX)

Common Issues and Fixes

Text appears black even after setting color

Ensure fill_format.fill_type = FillType.SOLID is set before assigning the color. Without setting the fill type, the color change may have no effect.

NullableBool.TRUE vs True

portion_format.font_bold expects NullableBool.TRUE, not the Python True. Assigning Python True may raise a TypeError or silently do nothing depending on the binding.

Font does not appear in the saved file

The latin_font property sets the Latin font family. If not set, the presentation theme font is used. Custom fonts must be embedded or available on the viewing machine.

Frequently Asked Questions

How do I change the font family?

Set portion_format.latin_font:

fmt.latin_font = slides.FontData("Arial")

FontData accepts the font family name as a string.

How do I set paragraph alignment?

Use paragraph_format.alignment:

from aspose.slides_foss import TextAlignment

tf.paragraphs[0].paragraph_format.alignment = TextAlignment.CENTER

Supported values: LEFT, CENTER, RIGHT, JUSTIFY.

How do I set line spacing?

Use paragraph_format.space_before (points before paragraph) or paragraph_format.space_after (points after paragraph):

tf.paragraphs[0].paragraph_format.space_before = 12   # 12pt before
tf.paragraphs[0].paragraph_format.space_after = 6     # 6pt after