[BUG] Formatting the Y axis when using MCAP to use K, M, B, T

[maxbrand99]

Requirements (place an x in each of the [ ])**

• I realize finplot is not a web lib. (Hint: it's native!)
• I've read the snippets and not found what I'm looking for.
• I've searched for any related issues and avoided creating a duplicate issue.
• I've updated finplot (pip install -U finplot).
• I've supplied the required data to run my code below.

Code to reproduce

import pandas as pd
import finplot as fplt
import json
import os
import pyqtgraph as pg

# Disable GUI for faster loading
os.environ['QT_QPA_PLATFORM'] = 'offscreen'
# IF LINUX, COMMENT LINE 10
os.environ['QT_QPA_FONTDIR'] = r'C:\Windows\Fonts'

fplt.right_margin_candles = 0
fplt.y_pad = 0.2
fplt.display_timezone = None

class MyAxis(fplt.EpochAxisItem):
    @staticmethod
    def my_timestamp_str(df, row):
        row = max(0, min(len(df) - 1, int(row)))
        timestamp = pd.to_datetime(df.iloc[row, 0], unit='ns')
        return timestamp.strftime('%H:%M')  # Returns HH:MM format
    
    def tickStrings(self, values, scale, spacing):
        return [self.my_timestamp_str(self.vb.datasrc.df, value) for value in values]

def format_number(value) -> str:
    try:
        num = float(value)
    except ValueError:
        return "Invalid number"
    if num >= 1_000_000_000_000:
        return f"{num / 1_000_000_000_000:.3g}T"
    elif num >= 1_000_000_000:
        return f"{num / 1_000_000_000:.3g}B"
    elif num >= 1_000_000:
        return f"{num / 1_000_000:.3g}M"
    elif num >= 1_000:
        return f"{num / 1_000:.3g}K"
    elif num >= 1:
        return f"{value:.4g}"
    else:
        return f"{value:.3f}"


def create_styled_chart(bars: dict, output_file: str, circulating_supply: float) -> None:
    # Prepare DataFrame
    pd.set_option("display.float_format", "{:.18f}".format)
    df = pd.DataFrame({
        'time': pd.to_datetime(bars['t'], unit='s'),
        'open': bars['o'],
        'high': bars['h'],
        'low': bars['l'],
        'close': bars['c'],
    }).set_index('time')
    
    # Create figure with 2 rows (price and volume)
    ax: pg.PlotItem = fplt.create_plot('Chart', rows=1, maximize=False)
    
    if circulating_supply is not None:
        ohlc_cols = ['open', 'high', 'low', 'close']
        df[ohlc_cols] *= float(circulating_supply)
        ax.setLabel('right', 'MCAP')
    
    # Set window size for better resolution
    ax.vb.win.resize(1200, 800)
    
    # set format for the X axis
    ax.setAxisItems({'bottom': MyAxis(vb=ax.vb, orientation='bottom')})
    # Create an InfiniteLine at the given position
    
    # hide the crosshair
    ax.crosshair.hide()
    
    # Set values and frame for the chart
    ax.showAxes([True, True, True, True], [False, False, True, True])
    
    # enable grid and set alpha
    ax.showGrid(x=True, y=True, alpha=0.1)
    
    # hide the top and left grids
    ax.getAxis('top').setGrid(False)
    ax.getAxis('left').setGrid(False)
    
    # Plot candlesticks
    fplt.candlestick_ochl(df[['open', 'close', 'high', 'low']], ax=ax)
    
    # Apply formatter to right axis of volume plot
    ax.getAxis('right').tickStrings = lambda values, scale, spacing: [format_number(v) for v in values]
    
    def _save_and_exit():
        fplt.screenshot(open(output_file, 'wb'))
        fplt.close()
    
    fplt.timer_callback(_save_and_exit, seconds=0.1)
    fplt.show()


def main():
    bars = json.load(open(f"bars.json"))
    create_styled_chart(bars, f"styled_chart.jpg", 1_000_000_000)


if __name__ == '__main__':
    main()

bars.json:

{"o": [0.283999852508, 0.335316021098, 0.295541710454, 0.321526110764, 0.295751925678, 0.397482936085, 0.36025548894, 0.428130186204, 0.441320792324, 0.552209600451, 0.573691129144, 0.580792552631, 0.521610668341, 0.532370994498, 0.46788489482, 0.419148639146, 0.447059378317, 0.453169495368, 0.522803840273, 0.421601984967, 0.417901389125, 0.51068540821, 0.497161087904, 0.443863724608, 0.553505185572, 0.508960883388, 0.761526640842, 0.754995142613, 0.880391127649, 0.890969376161, 0.801789866062, 0.916071353874, 0.80951055698, 0.896280586529, 0.835118288755, 0.732045774934, 0.815474444918, 0.896264109184, 0.932422892114, 1.12606377303, 1.09094673236, 1.1398783687, 1.02822370825, 1.03112195876, 1.07576263149, 1.09246931489, 1.1116746359, 1.24532289733, 1.19454079821, 1.15206579498, 1.0867928709, 1.08377382193, 1.13330242062, 1.08169465468, 1.01938177933, 1.24558067935, 1.37169098886, 1.42240748151, 1.34746115605, 1.37935255064, 1.4351511097, 1.32628096598, 1.29896404031, 1.18965733618, 1.20287185944, 1.35621850064, 1.20917283495, 1.29672335052, 1.40793906224, 1.55546428094, 1.4703519131, 1.43157601229, 1.45398698675, 1.38652366072, 1.36016159113, 1.29900160736, 1.20621595871, 1.0533751381, 1.07114391146, 1.14726256139, 1.14493403546, 1.03104168786, 0.941715549, 1.02963666573, 0.965012135571, 1.00355047532, 1.03566556244, 1.2245672824, 1.38734149458, 1.36031373323, 1.22487566318, 1.28677003061, 1.1886988897, 1.21055341119, 1.17927195424, 1.09724309769, 1.11964232466, 1.03823981734, 0.932901167229, 0.908358931056], "h": [0.34685074526, 0.357619711245, 0.349779955879, 0.321727431306, 0.414912818176, 0.414166126569, 0.43534829941, 0.4847923919, 0.554936379021, 0.64372886281, 0.601604914293, 0.639316769025, 0.596197991676, 0.543293018021, 0.47064430787, 0.486711904944, 0.461795263195, 0.548371166554, 0.56605970575, 0.447004632086, 0.541822377162, 0.540037430866, 0.498659596003, 0.56548109577, 0.61682381747, 0.784675462069, 0.781605422275, 0.983059742492, 0.963023267388, 0.904893253048, 0.961213968066, 0.948020601725, 0.964338037676, 0.93316895232, 0.841930989007, 0.823380729646, 0.899039525604, 0.936056575694, 1.20961603014, 1.19572310992, 1.16225839614, 1.15127445365, 1.0654732668, 1.12086837518, 1.23002117275, 1.16240610412, 1.26118003669, 1.28195052183, 1.22288136653, 1.15206579498, 1.12410942114, 1.14701927411, 1.14925339394, 1.12372687721, 1.24845397307, 1.44798511395, 1.43155494161, 1.43705552992, 1.4713148465, 1.46965405657, 1.46878576225, 1.35755079763, 1.33470449912, 1.21815000684, 1.35621850064, 1.37350352238, 1.32125888518, 1.44379131185, 1.57966083337, 1.64296345569, 1.50724363461, 1.45750577455, 1.47057945492, 1.46288799092, 1.38173488119, 1.3335609912, 1.21211361073, 1.1135909676, 1.17144946, 1.15223569906, 1.20532734852, 1.08354370266, 1.07741398747, 1.08678835669, 1.06390143666, 1.07357528693, 1.23989644346, 1.39212611693, 1.53185308762, 1.37723679914, 1.29682049758, 1.28742274162, 1.25690560548, 1.32012608433, 1.20476092308, 1.15399258445, 1.14157138577, 1.06030273369, 0.947677653178, 0.928658031], "l": [0.283999852508, 0.295524460264, 0.295541710454, 0.265781101456, 0.295315110585, 0.340318952906, 0.344593530017, 0.401455919429, 0.43314424089, 0.519425773993, 0.513122024324, 0.505115910819, 0.521208957143, 0.440888538781, 0.402799969073, 0.407427655699, 0.381975744651, 0.447832133229, 0.412067935659, 0.350227893197, 0.404288476458, 0.451582024067, 0.416022809911, 0.408300938373, 0.507788790573, 0.485570158322, 0.677862074035, 0.733972796222, 0.828759811989, 0.781307951215, 0.797821745992, 0.806258465888, 0.794614593878, 0.812026171491, 0.717259143057, 0.727244679083, 0.805842105199, 0.82540086068, 0.920877015273, 1.05867058053, 1.03426222429, 1.01435984701, 0.9928789557, 0.945852273791, 1.03819865566, 1.07430262274, 1.06575214816, 1.17858565969, 1.14783923588, 1.07207663884, 1.06391974019, 1.05385709949, 1.00480292847, 0.928153462418, 0.995654840939, 1.17343801238, 1.29614511106, 1.27375035673, 1.28440246069, 1.25029427929, 1.31151166178, 1.22204763246, 1.18294419305, 1.15790707724, 1.19333216204, 1.16322513993, 1.19048779591, 1.27627473973, 1.40187364855, 1.44874195485, 1.42980932345, 1.34266588442, 1.37696564217, 1.33867934237, 1.22476451021, 1.20559706662, 1.03314422721, 1.00301196915, 1.04099763069, 1.06731109929, 0.945830098462, 0.923458791612, 0.861326542087, 0.948907157797, 0.956734383002, 0.98573465499, 1.02226996552, 1.20164137857, 1.31606897826, 1.22022535749, 1.06643288081, 1.11923799594, 1.15539292172, 1.17927195424, 1.08585930531, 1.0464874611, 0.995616072297, 0.88152524569, 0.804031444601, 0.858044603758], "c": [0.335316021098, 0.295541710454, 0.321526110764, 0.295751925678, 0.397482936085, 0.36025548894, 0.428130186204, 0.441320792324, 0.552209600451, 0.573691129144, 0.580792552631, 0.521610668341, 0.532370994498, 0.46788489482, 0.419148639146, 0.447059378317, 0.453169495368, 0.522803840273, 0.421601984967, 0.417901389125, 0.51068540821, 0.497161087904, 0.443863724608, 0.553505185572, 0.508960883388, 0.761526640842, 0.754995142613, 0.880391127649, 0.890969376161, 0.801789866062, 0.916071353874, 0.80951055698, 0.896280586529, 0.835118288755, 0.732045774934, 0.815474444918, 0.896264109184, 0.932422892114, 1.12606377303, 1.09094673236, 1.1398783687, 1.02822370825, 1.03112195876, 1.07576263149, 1.09246931489, 1.1116746359, 1.24532289733, 1.19454079821, 1.15206579498, 1.0867928709, 1.08377382193, 1.13330242062, 1.08169465468, 1.01938177933, 1.24558067935, 1.37169098886, 1.42240748151, 1.34746115605, 1.37935255064, 1.4351511097, 1.32628096598, 1.29896404031, 1.18965733618, 1.20287185944, 1.35621850064, 1.20917283495, 1.29672335052, 1.40793906224, 1.55546428094, 1.4703519131, 1.43157601229, 1.45398698675, 1.38652366072, 1.36016159113, 1.29900160736, 1.20621595871, 1.0533751381, 1.07114391146, 1.14726256139, 1.14493403546, 1.03104168786, 0.941715549, 1.02963666573, 0.965012135571, 1.00355047532, 1.03566556244, 1.2245672824, 1.38734149458, 1.36031373323, 1.22487566318, 1.28677003061, 1.1886988897, 1.21055341119, 1.17927195424, 1.09724309769, 1.11964232466, 1.03823981734, 0.932901167229, 0.908358931056, 0.864512066055], "t": [1741996800, 1742083200, 1742169600, 1742256000, 1742342400, 1742428800, 1742515200, 1742601600, 1742688000, 1742774400, 1742860800, 1742947200, 1743033600, 1743120000, 1743206400, 1743292800, 1743379200, 1743465600, 1743552000, 1743638400, 1743724800, 1743811200, 1743897600, 1743984000, 1744070400, 1744156800, 1744243200, 1744329600, 1744416000, 1744502400, 1744588800, 1744675200, 1744761600, 1744848000, 1744934400, 1745020800, 1745107200, 1745193600, 1745280000, 1745366400, 1745452800, 1745539200, 1745625600, 1745712000, 1745798400, 1745884800, 1745971200, 1746057600, 1746144000, 1746230400, 1746316800, 1746403200, 1746489600, 1746576000, 1746662400, 1746748800, 1746835200, 1746921600, 1747008000, 1747094400, 1747180800, 1747267200, 1747353600, 1747440000, 1747526400, 1747612800, 1747699200, 1747785600, 1747872000, 1747958400, 1748044800, 1748131200, 1748217600, 1748304000, 1748390400, 1748476800, 1748563200, 1748649600, 1748736000, 1748822400, 1748908800, 1748995200, 1749081600, 1749168000, 1749254400, 1749340800, 1749427200, 1749513600, 1749600000, 1749686400, 1749772800, 1749859200, 1749945600, 1750032000, 1750118400, 1750204800, 1750291200, 1750377600, 1750464000, 1750550400]}

Describe the bug

It seems to not want to display correct letters on the Y axis. It instead only displays K even tho the number is in the billions (see expected image)

Expected behavior

Display K, M, B, T on the Y axis (for the example i gave, it should be M and B for millions and billions

Screenshots

If applicable, add screenshots to help explain your problem.
with the formatter:

without the formatter:

expected:

Reproducible in:

OS: Windows and Linux (if linux, comment out line 10)
finplot version: 1.9.7
pyqtgraph version: 0.13.7
pyqt5 version: 5.15.11
pyqt6 version: 6.9.1

[maxbrand99]

After some testing, it looks like its an issue with the scale factor, when running this code:

import pandas as pd
import finplot as fplt
import json
import os
import pyqtgraph as pg

# Disable GUI for faster loading
os.environ['QT_QPA_PLATFORM'] = 'offscreen'
# IF LINUX, COMMENT LINE 10
os.environ['QT_QPA_FONTDIR'] = r'C:\Windows\Fonts'

fplt.right_margin_candles = 0
fplt.y_pad = 0.2
fplt.display_timezone = None


class MyAxis(fplt.EpochAxisItem):
    @staticmethod
    def my_timestamp_str(df, row):
        row = max(0, min(len(df) - 1, int(row)))
        timestamp = pd.to_datetime(df.iloc[row, 0], unit='ns')
        return timestamp.strftime('%H:%M')  # Returns HH:MM format
    
    def tickStrings(self, values, scale, spacing):
        return [self.my_timestamp_str(self.vb.datasrc.df, value) for value in values]


class KMBTAxisItem(fplt.YAxisItem):
    """Custom Y axis item that formats numbers with K/M/B/T notation"""
    
    def tickStrings(self, values, scale, spacing):
        print(f"Raw values: {values}, Scale: {scale}")
        return [format_number(value * scale) for value in values]

def format_number(value) -> str:
    try:
        num = float(value)
    except ValueError:
        return "Invalid number"
    if num >= 1_000_000_000_000:
        return f"{num / 1_000_000_000_000:.3g}T"
    elif num >= 1_000_000_000:
        return f"{num / 1_000_000_000:.3g}B"
    elif num >= 1_000_000:
        return f"{num / 1_000_000:.3g}M"
    elif num >= 1_000:
        return f"{num / 1_000:.3g}K"
    elif num >= 1:
        return f"{value:.4g}"
    else:
        return f"{value:.3f}"


def create_styled_chart(bars: dict, output_file: str, circulating_supply: float) -> None:
    # Prepare DataFrame
    pd.set_option("display.float_format", "{:.18f}".format)
    df = pd.DataFrame({
        'time': pd.to_datetime(bars['t'], unit='s'),
        'open': bars['o'],
        'high': bars['h'],
        'low': bars['l'],
        'close': bars['c'],
    }).set_index('time')
    
    # Create figure with 2 rows (price and volume)
    ax: pg.PlotItem = fplt.create_plot('Chart', rows=1, maximize=False)
    
    if circulating_supply is not None:
        ohlc_cols = ['open', 'high', 'low', 'close']
        df[ohlc_cols] *= float(circulating_supply)
        ax.setLabel('right', 'MCAP')
    
    # Set window size for better resolution
    ax.vb.win.resize(1200, 800)
    
    # set format for the X axis
    ax.setAxisItems({'bottom': MyAxis(vb=ax.vb, orientation='bottom')})
    
    # Set custom Y axis formatter for K/M/B/T notation
    ax.setAxisItems({'right': KMBTAxisItem(vb=ax.vb, orientation='right')})
    
    # Create an InfiniteLine at the given position
    
    # hide the crosshair
    ax.crosshair.hide()
    
    # Set values and frame for the chart
    ax.showAxes([True, True, True, True], [False, False, True, True])
    
    # enable grid and set alpha
    ax.showGrid(x=True, y=True, alpha=0.1)
    
    # hide the top and left grids
    ax.getAxis('top').setGrid(False)
    ax.getAxis('left').setGrid(False)
    
    # Plot candlesticks
    fplt.candlestick_ochl(df[['open', 'close', 'high', 'low']], ax=ax)
    
    def _save_and_exit():
        fplt.screenshot(open(output_file, 'wb'))
        fplt.close()
    
    fplt.timer_callback(_save_and_exit, seconds=0.1)
    fplt.show()


def main():
    bars = json.load(open(f"bars.json"))
    create_styled_chart(bars, f"styled_chart.jpg", 1_000_000_000)


if __name__ == '__main__':
    main()

it prints out:

Raw values: [200.0, 400.0, 600.0, 800.0, 1000.0, 1200.0, 1400.0, 1600.0, 1800.0], Scale: 1.0
Raw values: [100.0, 300.0, 500.0, 700.0, 900.0, 1100.0, 1300.0, 1500.0, 1700.0], Scale: 1.0

when in reality, the scale factor should be 1_000_000 times that

[maxbrand99]

i found a solution for it,

    ax.getAxis('right').tickStrings = lambda values, scale, spacing: [format_number(v * ax.vb.yscale.scalef) for v in values]

its a really hacky workaround and i dislike it strongly, but for now, at least it works

[highfestiva]

Good catch, fixed in 29c9154 by adding a new function tick_string() which is called with the scaled values.