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Python 如何將 matplotlib 圖表整合進到PDF 中

2022-03-28 19:00:14

1.介紹

PDF 格式是與平臺無關,它獨立於底層作業系統和渲染引擎。事實上,PDF 是基於一種指令碼語言——PostScript,它是第一個獨立於裝置的頁面描述語言。

在本指南中,我們將使用 borb —— 一個專門用於閱讀、操作和生成 PDF 檔案的 Python 庫。它提供了一個低階模型(允許您存取精確的座標和佈局)和一個高階模型(您可以將邊距、位置等精確計算委託給佈局管理器) .

matplotlib 是一個資料視覺化庫,也是許多其他流行庫(如 Seaborn)背後的引擎。

基於用於建立報告(通常包括圖形)的常見 PDF 檔案,我們將看看如何使用 borbMatplotlib 圖表整合到 PDF 檔案中。

2.安裝 borb和 matplotlib

borb 可以從 GitHub 上的原始碼下載,或通過 pip 安裝:

$ pip install borb

matplotlib 也可以通過 pip 安裝:

$ pip install matplotlib

用 Borb 在 PDF 檔案中整合 Matplotlib 圖表

在建立餅圖等圖表之前,我們將編寫一個小的效用函數,該函數生成 N 種顏色,均勻分佈在顏色光譜中。

每當我們需要建立繪圖併為每個部分著色時,這將對我們有所幫助:

from borb.pdf.canvas.color.color import HSVColor, HexColor
from decimal import Decimal
import typing
 
def create_n_colors(n: int) -> typing.List[str]:
  # The base color is borb-blue
  base_hsv_color: HSVColor = HSVColor.from_rgb(HexColor("56cbf9"))
  # This array comprehension creates n HSVColor objects, transforms then to RGB, and then returns their hex string
  return [HSVColor(base_hsv_color.hue + Decimal(x / 360), Decimal(1), Decimal(1)).to_rgb().to_hex_string() for x in range(0, 360, int(360/n))]

HSL 和 HSV/HSB 是由計算機圖學研究人員在 1970 年代設計的,目的是更接近人類視覺感知色彩屬性的方式。在這些模型中,每種色調的顏色都排列在一個徑向切片中,圍繞中性色的中心軸,範圍從底部的黑色到頂部的白色:

用它表示顏色的優點是我們可以輕鬆地將顏色光譜分成相等的部分。

現在我們可以定義一個 create_pie_chart() 函數(或其他型別圖的函數):

# New import(s)
import matplotlib.pyplot as plt
from borb.pdf.canvas.layout.image.chart import Chart
from borb.pdf.canvas.layout.layout_element import Alignment
 
def create_piechart(labels: typing.List[str], data: typing.List[float]):
 
  # Symetric figure to ensure equal aspect ratio
  fig1, ax1 = plt.subplots(figsize=(4, 4))
  ax1.pie(
    data,
    explode=[0 for _ in range(0, len(labels))],
    labels=labels,
    autopct="%1.1f%%",
    shadow=True,
    startangle=90,
    colors=create_n_colors(len(labels)),
  )
 
  ax1.axis("equal")  # Equal aspect ratio ensures that pie is drawn as a circle.
 
  return Chart(
    plt.gcf(),
    width=Decimal(200),
    height=Decimal(200),
    horizontal_alignment=Alignment.CENTERED,
  )

在這裡,我們使用 Matplotlib 通過 pie() 函數建立餅圖。

PyPlot 範例的 gcf() 函數返回當前圖形。該圖可以嵌入到 PDF 檔案中,方法是將其注入到 Chart 建構函式中,並與您的自定義引數(例如width, height 和 horizontal_alignment)一起插入。

我們只需向Chart建構函式提供一個 Matplotlib 圖。

3.將 Matplotlib 圖表新增到 PDF 檔案

現在是時候建立我們的 PDF 檔案並向其中新增內容了。

# New import(s)
from borb.pdf.document import Document
from borb.pdf.page.page import Page
from borb.pdf.pdf import PDF
from borb.pdf.canvas.layout.page_layout.multi_column_layout import MultiColumnLayout
from borb.pdf.canvas.layout.page_layout.page_layout import PageLayout
from borb.pdf.canvas.layout.text.paragraph import Paragraph
 
# Create empty Document
pdf = Document()
 
# Create empty Page
page = Page()
 
# Add Page to Document
pdf.append_page(page)
 
# Create PageLayout
layout: PageLayout = MultiColumnLayout(page)
 
# Write title
layout.add(Paragraph("About Lorem Ipsum", 
                     font_size=Decimal(20), 
                     font="Helvetica-Bold"))

我們將在此 PDF 中使用連字元,以確保文字的佈局更加流暢。borb 中的連字元非常簡單:

# New import(s)
from borb.pdf.canvas.layout.hyphenation.hyphenation import Hyphenation
 
# Create hyphenation algorithm
hyphenation_algorithm: Hyphenation = Hyphenation("en-gb")
 
# Write paragraph
layout.add(Paragraph(
    """
    Lorem Ipsum is simply dummy text of the printing and typesetting industry. 
    Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, 
    when an unknown printer took a galley of type and scrambled it to make a type specimen book. 
    It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. 
    It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, 
    and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
    """, text_alignment=Alignment.JUSTIFIED, hyphenation=hyphenation_algorithm))

現在我們可以使用我們之前宣告的函數新增餅圖;

# Write graph
layout.add(create_piechart(["Loren", "Ipsum", "Dolor"], 
                           [0.6, 0.3, 0.1]))

接下來我們將編寫另外三個 Paragraph物件。其中一個將不僅僅表示參照(側面邊框,不同字型等)。

# Write paragraph
layout.add(Paragraph(
    """
    Contrary to popular belief, Lorem Ipsum is not simply random text. 
    It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old. 
    Richard McClintock, a Latin professor at Hampden-Sydney College in Virginia, looked up one of the more obscure Latin words, 
    consectetur, from a Lorem Ipsum passage, and going through the cites of the word in classical literature, 
    discovered the undoubtable source.
    """, text_alignment=Alignment.JUSTIFIED, hyphenation=hyphenation_algorithm))
 
# Write paragraph
layout.add(Paragraph(
    """
    Lorem Ipsum is simply dummy text of the printing and typesetting industry. 
    """, 
    font="Courier-Bold",
    text_alignment=Alignment.JUSTIFIED, 
    hyphenation=hyphenation_algorithm,
    border_color=HexColor("56cbf9"),
    border_width=Decimal(3),
    border_left=True,
    padding_left=Decimal(5),
    padding_bottom=Decimal(5),
))
 
# Write paragraph
layout.add(Paragraph(
    """
    Lorem Ipsum comes from sections 1.10.32 and 1.10.33 of "de Finibus Bonorum et Malorum" 
    (The Extremes of Good and Evil) by Cicero, written in 45 BC. 
    This book is a treatise on the theory of ethics, very popular during the Renaissance.
    """, text_alignment=Alignment.JUSTIFIED, hyphenation=hyphenation_algorithm))

讓我們新增另一個繪圖。

# Write graph
layout.add(create_piechart(["Loren", "Ipsum", "Dolor", "Sit", "Amet"], 
                           [600, 30, 89, 100, 203]))

還有一段內容(Paragraph):

# Write paragraph
layout.add(Paragraph(
    """
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. 
    The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', 
    making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, 
    and a search for 'lorem ipsum' will uncover many web sites still in their infancy. 
    Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
    """, text_alignment=Alignment.JUSTIFIED, hyphenation=hyphenation_algorithm))

最後,我們可以儲存檔案(Document):

# Write to disk
with open("output.pdf", "wb") as pdf_file_handle:
  PDF.dumps(pdf_file_handle, pdf)

執行此程式碼會生成如下所示的 PDF 檔案:

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